START-INFO-DIR-ENTRY * mysql: (mysql). *MySQL* documentation. END-INFO-DIR-ENTRY This is a manual for *MySQL*. This version is about the 3.22.27 version of *MySQL*. For a *3.20* version see the relevant distribution. General Information about MySQL ******************************* This is the *MySQL* reference manual; it documents *MySQL* version 3.22.27. *MySQL* is a very fast, multi-threaded, multi-user and robust SQL (Structured Query Language) database server. For Unix and OS/2 platforms, *MySQL* is basically free; for Microsoft platforms you must get a *MySQL* license after a trial time of 30 days. *Note Licensing and Support::. The *MySQL* home page (http://www.mysql.com/) provides the latest information about *MySQL*. For a discussion of *MySQL*'s capabilities, see *Note Features::. For installation instructions, see *Note Installing::. For tips on porting *MySQL* to new machines or operating systems, see *Note Porting::. For information about upgrading from a 3.21 release, see *Note Upgrading-from-3.21::. For a tutorial introduction to MySQL, see *Note Tutorial::. For examples of SQL and benchmarking information, see the benchmarking directory. For source distributions, this is the `bench' directory. For binary distributions, this is the `sql-bench' directory. For a history of new features and bug fixes, see *Note News::. For a list of currently known bugs and misfeatures, see *Note Bugs::. For future plans, see *Note TODO::. For a list of all the contributors to this product, see *Note Credits::. *IMPORTANT:* Send bug (error) reports, questions and comments to the mailing list at . *Note Bug reports::. For source distributions, the `mysqlbug' script can be found in the `scripts' directory. For binary distributions, `mysqlbug' can be found in the `bin' directory. If you have any suggestions concerning additions or corrections to this manual, please send them to the *MySQL* mailing list () with the following subject line: `documentation suggestion: [Insert Topic Here]'. *Note Mailing-list::. What is MySQL? ============== *MySQL* is a true multi-user, multi-threaded SQL database server. SQL is the most popular database language in the world. *MySQL* is a client/server implementation that consists of a server daemon `mysqld' and many different client programs and libraries. SQL is a standardized language that makes it easy to store, update and access information. For example, you can use SQL to retrieve product information and store customer information for a web site. *MySQL* is also fast and flexible enough to allow you to store logs and pictures in it. The main goals of *MySQL* are speed, robustness and ease of use. *MySQL* was originally developed because we at TcX needed a SQL server that could handle very large databases an order of magnitude faster than what any database vendor could offer to us. We have now been using *MySQL* since 1996 in an environment with more than 40 databases containing 10,000 tables, of which more than 500 have more than 7 million rows. This is about 100 gigabytes of mission-critical data. The base upon which *MySQL* is built is a set of routines that have been used in a highly demanding production environment for many years. Although *MySQL* is still under development, it already offers a rich and highly useful function set. The official way to pronounce *MySQL* is "My Ess Que Ell" (Not MY-SEQUEL). About this manual ================= This manual is currently available in Texinfo, plain text, Info, HTML, PostScript and PDF versions. Because of their size, PostScript and PDF versions are not included with the main *MySQL* distribution, but are available for separate download at `http://www.mysql.com'. The primary document is the Texinfo file. The HTML version is produced automatically with a modified version of `texi2html'. The plain text and Info versions are produced with `makeinfo'. The Postscript version is produced using `texi2dvi' and `dvips'. The PDF version is produced with the Ghostscript utility `ps2pdf'. This manual is written and maintained by David Axmark, Michael (Monty) Widenius, Paul DuBois and Kim Aldale. For other contributors, see *Note Credits::. Conventions used in this manual ------------------------------- This manual uses certain typographical conventions: `constant' Constant-width font is used for command names and options; SQL statements; database, table and column names; C and Perl code; and environment variables. Example: "To see how `mysqladmin' works, invoke it with the `--help' option." `filename' Constant-width font with surrounding quotes is used for filenames and pathnames. Example: "The distribution is installed under the `/usr/local/' directory." `c' Constant-width font with surrounding quotes is also used to indicate character sequences. Example: "To specify a wildcard, use the `%' character." *italic* Italic font is used for emphasis, *like this*. *boldface* Boldface font is used for access privilege names (e.g., "do not grant the *process* privilege lightly") and to convey *especially strong emphasis*. When commands are shown that are meant to be executed by a particular program, the program is indicated by the prompt shown with the command. For example, `shell>' indicates a command that you execute from your login shell, and `mysql>' indicates a command that you execute from the `mysql' client: shell> type a shell command here mysql> type a mysql command here Shell commands are shown using Bourne shell syntax. If you are using a `csh'-style shell, you may need to issue commands slightly differently. For example, the sequence to set an environment variable and run a command looks like this in Bourne shell syntax: shell> VARNAME=value some_command For `csh', you would execute the sequence like this: shell> setenv VARNAME value shell> some_command Database, table and column names often must be substituted into commands. To indicate that such substitution is necessary, this manual uses `db_name', `tbl_name' and `col_name'. For example, you might see a statement like this: mysql> SELECT col_name FROM db_name.tbl_name; This means that if you were to enter a similar statement, you would supply your own database, table and column names, perhaps like this: mysql> SELECT author_name FROM biblio_db.author_list; SQL statements may be written in uppercase or lowercase. When this manual shows a SQL statement, uppercase is used for particular keywords if those keywords are under discussion (to emphasize them) and lowercase is used for the rest of the statement. So you might see the following in a discussion of the `SELECT' statement: mysql> SELECT count(*) FROM tbl_name; On the other hand, in a discussion of the `COUNT()' function, the statement would be written like this: mysql> select COUNT(*) from tbl_name; If no particular emphasis is intended, all keywords are written uniformly in uppercase. In syntax descriptions, square brackets (`[' and `]') are used to indicate optional words or clauses: DROP TABLE [IF EXISTS] tbl_name When a syntax element consists of a number of alternatives, the alternatives are separated by vertical bars (`|'). When one member from a set of choices may be chosen, the alternatives are listed within square brackets. When one member from a set of choices must be chosen, the alternatives are listed within braces (`{' and `}'): TRIM([[BOTH | LEADING | TRAILING] [remstr] FROM] str) {DESCRIBE | DESC} tbl_name {col_name | wild} History of MySQL ================ We once started off with the intention of using `mSQL' to connect to our tables using our own fast low-level (ISAM) routines. However, after some testing we came to the conclusion that `mSQL' was not fast enough or flexible enough for our needs. This resulted in a new SQL interface to our database but with almost the same API interface as `mSQL'. This API was chosen to ease porting of third-party code. The derivation of the name *MySQL* is not perfectly clear. Our base directory and a large number of our libraries and tools have had the prefix "my" for well over 10 years. However, Monty's daughter (some years younger) is also named My. So which of the two gave its name to *MySQL* is still a mystery, even for us. The main features of MySQL ========================== The following list describes some of the important characteristics of *MySQL*: * Fully multi-threaded using kernel threads. That means it easily can use multiple CPUs if available. * C, C++, Eiffel, Java, Perl, PHP, Python and TCL APIs. *Note Clients::. * Works on many different platforms. *Note Which OS::. * Many column types: signed/unsigned integers 1, 2, 3, 4 and 8 bytes long, `FLOAT', `DOUBLE', `CHAR', `VARCHAR', `TEXT', `BLOB', `DATE', `TIME', `DATETIME', `TIMESTAMP', `YEAR', `SET' and `ENUM' types. *Note Column types::. * Very fast joins using an optimized one-sweep multi-join. * Full operator and function support in the `SELECT' and `WHERE' parts of queries. Example: mysql> SELECT CONCAT(first_name, " ", last_name) FROM tbl_name WHERE income/dependents > 10000 AND age > 30; * SQL functions are implemented through a highly-optimized class library and should be as fast as they can get! Usually there shouldn't be any memory allocation at all after query initialization. * Full support for SQL `GROUP BY' and `ORDER BY' clauses. Support for group functions (`COUNT()', `COUNT(DISTINCT)', `AVG()', `STD()', `SUM()', `MAX()' and `MIN()'). * Support for `LEFT OUTER JOIN' with ANSI SQL and ODBC syntax. * You can mix tables from different databases in the same query (as of version 3.22). * A privilege and password system which is very flexible and secure, and which allows host-based verification. Passwords are secure since all password traffic when connecting to a server is encrypted. * ODBC (Open-DataBase-Connectivity) for Windows95 (with source). All ODBC 2.5 functions and many others. You can, for example, use Access to connect to your *MySQL* server. *Note ODBC::. * Very fast B-tree disk tables with index compression. * 16 indexes per table are allowed. Each index may consist of 1 to 16 columns or parts of columns. The maximum index length is 256 bytes (this may be changed when compiling *MySQL*). An index may use a prefix of a `CHAR' or `VARCHAR' field. * Fixed-length and variable-length records. * In-memory hash tables which are used as temporary tables. * Handles large databases. We are using *MySQL* with some databases that contain 50,000,000 records. * All columns have default values. You can use `INSERT' to insert a subset of a table's columns; those columns that are not explicitly given values are set to their default values. * Uses GNU Automake, Autoconf, and `libtool' for portability. * Written in C and C++. Tested with a broad range of different compilers. * A very fast thread-based memory allocation system. * No memory leaks. Tested with a commercial memory leakage detector (`purify'). * Includes `isamchk', a very fast utility for table checking, optimization and repair. *Note Maintenance::. * Full support for the ISO-8859-1 Latin1 character set. For example, the Scandinavian characters *a, "a and "o are allowed in table and column names. * All data are saved in ISO-8859-1 Latin1 format. All comparisons for normal string columns are case insensitive. * Sorting is done according to the ISO-8859-1 Latin1 character set (the Swedish way at the moment). It is possible to change this in the source by adding new sort order arrays. To see an example of very advanced sorting, look at the Czech sorting code. *MySQL* supports many different character sets that can be specified at compile time. * Aliases on tables and columns as in the SQL92 standard. * `DELETE', `INSERT', `REPLACE', and `UPDATE' return how many rows were changed (affected). * Function names do not clash with table or column names. For example, `ABS' is a valid column name. The only restriction is that for a function call, no spaces are allowed between the function name and the `(' that follows it. *Note Reserved words::. * All *MySQL* programs can be invoked with the `--help' or `-?' options to obtain online assistance. * The server can provide error messages to clients in many languages. *Note Languages::. * Clients connect to the *MySQL* server using TCP/IP connections or Unix sockets, or named pipes under NT. * The *MySQL*-specific `SHOW' command can be used to retrieve information about databases, tables and indexes. The `EXPLAIN' command can be used to determine how the optimizer resolves a query. How stable is MySQL? ==================== This section addresses the questions, "how stable is *MySQL*?" and, "can I depend on *MySQL* in this project?" Here we will try to clarify some issues and to answer some of the more important questions that seem to concern many people. This section has been put together from information gathered from the mailing list (which is very active in reporting bugs). At TcX, *MySQL* has worked without any problems in our projects since mid-1996. When *MySQL* was released to a wider public, we noticed that there were some pieces of "untested code" that were quickly found by the new users who made queries in a manner different than our own. Each new release has had fewer portability problems than the previous one (even though each has had many new features), and we hope that it will be possible to label one of the next releases "stable". Each release of *MySQL* has been usable and there have been problems only when users start to use code from "the gray zones". Naturally, outside users can't know what the gray zones are; this section attempts to indicate those that are currently known. The descriptions deal with the 3.22.x version of *MySQL*. All known and reported bugs are fixed in the latest version, with the exception of the bugs listed in the bugs section, which are things that are "design"-related. *Note Bugs::. *MySQL* is written in multiple layers and different independent modules. These modules are listed below with an indication of how well-tested each of them is: *The ISAM table handler -- Stable* This manages storage and retrieval of all data in *MySQL* 3.22 and earlier versions. In all *MySQL* releases there hasn't been a single (reported) bug in this code. The only known way to get a corrupted table is to kill the server in the middle of an update. Even that is unlikely to destroy any data beyond rescue, because all data are flushed to disk between each query. There hasn't been a single bug report about lost data because of bugs in *MySQL*, either. *The MyISAM table handler -- Beta* This is new in *MySQL* 3.23. It's largely based on the ISAM table code but has a lot of new very useful features. *The parser and lexical analyser -- Stable* There hasn't been a single reported bug in this system for a long time. *The C client code -- Stable* No known problems. In early 3.20 releases, there were some limitations in the send/receive buffer size. As of 3.21.x, the buffer size is now dynamic up to a default of 24M. *Standard client programs -- Stable* These include `mysql', `mysqladmin' and `mysqlshow', `mysqldump', and `mysqlimport'. *Basic SQL -- Stable* The basic SQL function system and string classes and dynamic memory handling. Not a single reported bug in this system. *Query optimizer -- Stable* *Range optimizer -- Gamma* *Join optimizer -- Stable* *Locking -- Gamma* This is very system-dependent. On some systems there are big problems using standard OS locking (`fcntl()'). In these cases, you should run the *MySQL* daemon with the `--skip-locking' flag. Problems are known to occur on some Linux systems and on SunOS when using NFS-mounted file systems. *Linux threads -- Gamma* The only problem found has been with the `fcntl()' call, which is fixed by using the `--skip-locking' option to `mysqld'. Some people have reported lockup problems with the 0.5 release. *Solaris 2.5+ pthreads -- Stable* We use this for all our production work. *MIT-pthreads (Other systems) -- Gamma* There have been no reported bugs since 3.20.15 and no known bugs since 3.20.16. On some systems, there is a "misfeature" where some operations are quite slow (a 1/20 second sleep is done between each query). Of course, MIT-pthreads may slow down everything a bit, but index-based `SELECT' statements are usually done in one time frame so there shouldn't be a mutex locking/thread juggling. *Other thread implementions -- Alpha - Beta* The ports to other systems are still very new and may have bugs, possibly in *MySQL*, but most often in the thread implementation itself. *`LOAD DATA ...', `INSERT ... SELECT' -- Stable* Some people have thought they have found bugs here, but these usually have turned out to be misunderstandings. Please check the manual before reporting problems! *`ALTER TABLE' -- Stable* Small changes in 3.22.12. *DBD -- Stable* Now maintained by Jochen Wiedmann . Thanks! *`mysqlaccess' -- Stable* Written and maintained by Yves Carlier . Thanks! *`GRANT' -- Gamma* Big changes made in *MySQL* 3.22.12. **MyODBC* (uses ODBC SDK 2.5) -- Beta* It seems to work well with some programs. TcX provides email support for paying customers, but the *MySQL* mailing list usually provides answers to common questions. Bugs are usually fixed right away with a patch; for serious bugs, there is almost always a new release. Year 2000 compliance ==================== *MySQL* itself has no problems with Year 2000 (Y2K) compliance: * *MySQL* uses Unix time functions and has no problems with dates until `2069'; all 2-digit years are regarded to be in the range `1970' to `2069', which means that if you store `01' in a `year' column, *MySQL* treats it as `2001'. * All *MySQL* date functions are stored in one file `sql/time.cc' and coded very carefully to be year 2000-safe. * In *MySQL* 3.22 and later versions, the new `YEAR' column type can store years `0' and `1901' to `2155' in 1 byte and display them using 2 or 4 digits. You may run into problems with applications that use *MySQL* in a way that is not Y2K-safe. For example, many old applications store or manipulate years using 2-digit values (which are ambiguous) rather than 4-digit values. This problem may be compounded by applications that use values such as `00' or `99' as "missing" value indicators. Unfortunately, these problems may be difficult to fix, since different applications may be written by different programmers, each of whom may use a different set of conventions and date-handling functions. Here is a simple demonstration illustrating that *MySQL* doesn't have any problems with dates until the year 2030! mysql> DROP TABLE IF EXISTS y2k; mysql> CREATE TABLE y2k (date date, date_time datetime, time_stamp timestamp); mysql> INSERT INTO y2k VALUES ("1998-12-31","1998-12-31 23:59:59",19981231235959); mysql> INSERT INTO y2k VALUES ("1999-01-01","1999-01-01 00:00:00",19990101000000); mysql> INSERT INTO y2k VALUES ("1999-09-09","1999-09-09 23:59:59",19990909235959); mysql> INSERT INTO y2k VALUES ("2000-01-01","2000-01-01 00:00:00",20000101000000); mysql> INSERT INTO y2k VALUES ("2000-02-28","2000-02-28 00:00:00",20000228000000); mysql> INSERT INTO y2k VALUES ("2000-02-29","2000-02-29 00:00:00",20000229000000); mysql> INSERT INTO y2k VALUES ("2000-03-01","2000-03-01 00:00:00",20000301000000); mysql> INSERT INTO y2k VALUES ("2000-12-31","2000-12-31 23:59:59",20001231235959); mysql> INSERT INTO y2k VALUES ("2001-01-01","2001-01-01 00:00:00",20010101000000); mysql> INSERT INTO y2k VALUES ("2004-12-31","2004-12-31 23:59:59",20041231235959); mysql> INSERT INTO y2k VALUES ("2005-01-01","2005-01-01 00:00:00",20050101000000); mysql> INSERT INTO y2k VALUES ("2030-01-01","2030-01-01 00:00:00",20300101000000); mysql> INSERT INTO y2k VALUES ("2050-01-01","2050-01-01 00:00:00",20500101000000); mysql> SELECT * FROM y2k; +------------+---------------------+----------------+ | date | date_time | time_stamp | +------------+---------------------+----------------+ | 1998-12-31 | 1998-12-31 23:59:59 | 19981231235959 | | 1999-01-01 | 1999-01-01 00:00:00 | 19990101000000 | | 1999-09-09 | 1999-09-09 23:59:59 | 19990909235959 | | 2000-01-01 | 2000-01-01 00:00:00 | 20000101000000 | | 2000-02-28 | 2000-02-28 00:00:00 | 20000228000000 | | 2000-02-29 | 2000-02-29 00:00:00 | 20000229000000 | | 2000-03-01 | 2000-03-01 00:00:00 | 20000301000000 | | 2000-12-31 | 2000-12-31 23:59:59 | 20001231235959 | | 2001-01-01 | 2001-01-01 00:00:00 | 20010101000000 | | 2004-12-31 | 2004-12-31 23:59:59 | 20041231235959 | | 2005-01-01 | 2005-01-01 00:00:00 | 20050101000000 | | 2030-01-01 | 2030-01-01 00:00:00 | 20300101000000 | | 2050-01-01 | 2050-01-01 00:00:00 | 00000000000000 | +------------+---------------------+----------------+ 13 rows in set (0.00 sec) This shows that the `DATE' and `DATETIME' types are will not give any problems with future dates (they handle dates until the year 9999). The `TIMESTAMP' type, that is used to store the current time, has a range up to only `2030-01-01'. `TIMESTAMP' has a range of `1970' to `2030' on 32-bit machines (signed value). On 64-bit machines it handles times up to `2106' (unsigned value). Even though *MySQL* is Y2K-compliant, it is your responsibility to provide unambiguous input. See *Note Y2K issues:: for *MySQL*'s rules for dealing with ambiguous date input data (data containing 2-digit year values). General SQL information and tutorials ===================================== This book has been recommended by a several people on the *MySQL* mailing list: Judith S. Bowman, Sandra L. Emerson and Marcy Darnovsky The Practical SQL Handbook: Using Structured Query Language Second Edition Addison-Wesley ISBN 0-201-62623-3 http://www.awl.com This book has also received some recommendations on the mailing list: Martin Gruber Understanding SQL ISBN 0-89588-644-8 Publisher Sybex 510 523 8233 Alameda, CA USA A SQL tutorial is available on the net at `http://www.geocities.com/SiliconValley/Vista/2207/sql1.html' SQL in 21 Tagen (online book in German language): `http://www.mut.de/leseecke/buecher/sql/inhalt.htm' Useful MySQL-related links ========================== Commercial applications that support MySQL ------------------------------------------ * SupportWizard; Interactive helpdesk on the web (This product includes a licensed copy of MySQL) (http://www.supportwizard.com/) * Right Now Web; Web automation for customer service (http://www.rightnowtech.com/) * Bazaar; Interactive Discussion Forums with web interface (http://www.icaap.org/Bazaar/) * PhoneSweepT (http://www.phonesweep.com/) is the world's first commercial Telephone Scanner. Many break-ins in recent years have come not through the Internet, but through unauthorized dial-up modems. PhoneSweep lets you find these modems by repeatedly placing phone calls to every phone number that your organization controls. PhoneSweep has a built-in expert system that can recognize more than 250 different kinds of remote-access programs, including Carbon CopyT, pcANYWHERET, and Windows NT RAS. All information is stored in the SQL database. It then generates a comprehensive report detailing which services were discovered on which dial-up numbers in your organization. SQL Clients ----------- * *MySQL* Editor/Utility for MS Windows Platforms. (http://www.urbanresearch.com/software/utils/urbsql/index.html) * KDE MySQL client (http://www.etu.info.unicaen.fr/~fbilhaut/kmysql/) * Kiosk; a MySQL client for database management (http://www.icaap.org/software/kiosk/). Written in Perl. Will be a part of Bazaar. Web development tools that support *MySQL* ------------------------------------------ * PHP: A server-side HTML-embedded scripting language (http://www.php.net/) * The Midgard Application Server; a powerful Web development environment based on MySQL and PHP (http://www.midgard-project.org) * SmartWorker is a platform for web application development (http://www.smartworker.org) * XSP: e(X)tendible (s)erver (p)ages and is a HTML embedded tag language written in Java (previously known as XTAGS) (http://xsp.lentus.se/) * dbServ (http://www.dbServ.de/) is an extension to a web server to integrate databases output into your HTML code. You may use any HTML function in your output. Only the client will stop you. It works as standalone server or as JAVA servlet. * Platform independent ASP from Chili!Soft (http://www.chilisoft.com/) * *MySQL* + PHP demos (http://www.wernhart.priv.at/php/) * ForwardSQL: HTML interface to manipulate *MySQL* databases (http://www.dbwww.com/) * WWW-SQL: Display database information (http://www.daa.com.au/~james/www-sql/) * Minivend: A Web shopping cart (http://www.minivend.com/minivend/) * HeiTML: A server-side extension of HTML and a 4GL language at the same time (http://www.heitml.com/) * Metahtml: A Dynamic Programming Language for WWW Applications (http://www.metahtml.com/) * VelocityGen for Perl and TCL (http://www.binevolve.com/) * Hawkeye Internet Server Suite (http://hawkeye.net/) * Network Database Connection For Linux (http://www.fastflow.com/) * WDBI: Web browser as a universal front end to databases which supports *MySQL* well. (http://www.wdbi.net/) * WebGroove Script: HTML compiler and server-side scripting language (http://www.webgroove.com/) * A server-side web site scripting language (http://www.ihtml.com/) * How to use *MySQL* with Coldfusion on Solaris (ftp://ftp.igc.org/pub/myodbc/README) * Calistra's ODBC *MySQL* Administrator (http://calistra.com/MySQL/) * Webmerger (http://www.webmerger.com) This CGI tool interprets files and generates dynamic output based on a set of simple tags. Ready-to-run drivers for *MySQL* and PostgreSQL through ODBC. * PHPclub (http://phpclub.unet.ru/index_e.php3). Tips and tricks for PHP * MySQL and Perl Scripts (http://www.penguinservices.com/scripts) * The Widgetchuck; Web Site Tools and Gadgets (http://www.widgetchuck.com) * AdCycle (http://www.adcycle.com/) advertising management software Databse design tools with MySQL support --------------------------------------- * "Dezign for databases" is a database development tool using an rick> entity relationship diagram (ERD). (http://www.heraut.demon.nl/dezign/dezign.html) Web servers with *MySQL* tools ------------------------------ * An Apache authentication module (http://bourbon.netvision.net.il/mysql/mod_auth_mysql/) * The Roxen Challenger Web server (http://www.roxen.com/) Extensions for other programs ----------------------------- A Delphi interface to *MySQL*. (http://www.fichtner.net/delphi/mysql.delphi.phtml) With source code. By Matthias Fichtner. * *TmySQL*; A library to use *MySQL* with Delphi (http://www.productivity.org/projects/mysql/) * Delphi TDataset-component (http://www.geocities.com/CapeCanaveral/2064/mysql.html) * Support for BIND (The Internet Domain Name Server) (http://www.seawood.org/msql_bind/) * Sendmail extensions using MySQL (http://paul.colba.net) *ODBC* related links -------------------- * Popular iODBC Driver Manager (libiodbc) now available in Open Source format (http://www.iodbc.org/) * The FreeODBC Pages (http://users.ids.net/~bjepson/freeODBC/) *API* related links ------------------- * www.jppp.com (http://www.jppp.com) Partially implemented TDataset-compatible components for *MySQL*. * qpopmysql (http://www.riverstyx.net/qpopmysql/) A patch to allow POP3 authentication from a *MySQL* database. There's also a link to Paul Khavkine's patch for Procmail to allow any MTA to deliver to users in a *MySQL* database. * Visual Basic class generator for Active X (http://www.pbc.ottawa.on.ca) * Client libraries for the Macintosh (http://www.lilback.com/macsql/) * *MySQL* binding to Free Pascal (http://tfdec1.fys.kuleuven.ac.be/~michael/fpc-linux/mysql) Other *MySQL*-related links --------------------------- * Registry of Web providers who support *MySQL* (http://www.wix.com/mysql-hosting) Links about using *MySQL* in Japan/Asia (http://www.softagency.co.jp/mysql/index.en.phtml) * Commercial Web defect tracking system (http://www.open.com.au/products.html) * PTS: Project Tracking System (http://www.stonekeep.com/pts/) * Job and software tracking system (http://tomato.nvgc.vt.edu/~hroberts/mot) * ExportSQL: A script to export data from Access95+ (http://www.cynergi.net/non-secure/exportsql/) * SAL (Scientific Applications on Linux) *MySQL* entry (http://SAL.KachinaTech.COM/H/1/MYSQL.html) * A consulting company which mentions *MySQL* in the right company (http://www.infotech-nj.com/itech/index.shtml) * PMP Computer Solutions. Database developers using *MySQL* and `mSQL' (http://www.pmpcs.com/) * Airborne Early Warning Association (http://www.aewa.org) * *MySQL* UDF Registry (http://abattoir.cc.ndsu.nodak.edu/~nem/mysql/udf/) * Y2K tester (http://21ccs.com/~gboersm/y2kmatrix/) SQL and database interfaces --------------------------- * KMySQL (http://www.penguinpowered.com/~kmysql) KMySQL is a database client for KDE that primarily supports *MySQL*. * The JDBC database access API (http://java.sun.com/products/jdbc/) * Patch for `mSQL' TCL (http://www.gagme.com/mysql) * EasySQL: An ODBC-like driver manager (http://www.amsoft.ru/easysql/) * A REXX interface to SQL databases (http://www.lightlink.com/hessling/rexxsql.html) * TCL interface (http://www.binevolve.com/~tdarugar/tcl-sql) Examples of MySQL use --------------------- * Little6 Inc (http://www.little6.com/about/linux/) An online contract and job finding site that is powered by *MySQL*, PHP3 and Linux. * DELECis (http://www.delec.com/is/products/prep/examples/BookShelf/index.html) A tool which makes it very easy to create an automatically generated table documentation. They have used *MySQL* as an example. * Steve Fambro (http://shredder.elen.utah.edu/steve.html) Uses *MySQL* and webmerger. There is an employee database, and a license plate database with all of the registered Utah vehicles (over 1.2 million). The License plate field is indexed.....so the *searches* are instantaneous. * World Records (http://www.worldrecords.com) A search engine for information about music that uses *MySQL* and PHP. * Examples using *MySQL*; (check Top 10) (http://webdev.berber.co.il/) * A Contact Database using *MySQL* and PHP (http://www.webtechniques.com/features/1998/01/note/note.shtml) * Web based interface and Community Calender with PHP (http://modems.rosenet.net/mysql/) * Perl package to generate html from a SQL table structure and for generating SQL statements from an html form. (http://www.odbsoft.com/cook/sources.htm) * Basic telephone database using `DBI'/`DBD' (http://www.gusnet.cx/proj/telsql/). * Installing new Perl modules that require locally installed modules (http://www.iserver.com/support/contrib/perl5/modules.html) * JDBC examples by Daniel K. Schneider (http://tecfa.unige.ch/guides/java/staf2x/ex/jdbc/coffee-break) * SQL BNF (http://www.spade.com/linux/howto/PostgreSQL-HOWTO-41.html) * Object Oriented Concepts Inc; CORBA applications with examples in source (http://www.ooc.com/) * DBWiz; Includes an example of how to manage own cursors in VB (http://www.pbc.ottawa.on.ca/) * Pluribus (http://keilor.cs.umass.edu/pluribus/) Pluribus, is a free search engine that learns to improve the quality of its results over time. Pluribus works by recording which pages a user prefers among those returned for a query. A user votes for a page by selecting it; Pluribus then uses that knowledge to improve the quality of the results when someone else submits the same (or similar) query. Uses PHP and *MySQL*. * Stopbit (http://www.stopbit.com/) A technology news site using *MySQL* and PHP * Example scripts at Jokes2000 (http://www.jokes2000.com/scripts/) * *MySQL*-perl tutorial (http://www.hotwired.com/webmonkey/backend/tutorials/tutorial1.html) * PHP/MySQL Tutorial (http://www.hotwired.com/webmonkey/databases/tutorials/tutorial4.html) * FutureForum Web Discussion Software (http://futurerealm.com/forum/futureforum.cgi) * `http://www.linuxsupportline.com/~kalendar/ KDE based calendar manager' The calendar manager has both single user (file based) and multi user (*MySQL* database) support. * Example of storing/retrieving images with *MySQL* and CGI (http://tim.desert.net/~tim/imger/) * Online shopping cart system (http://www.penguinservices.com/scripts) * Old Photo Album (http://www.city-gallery.com/album/) The album is a collaborative popular history of photography project that generates all pages from data stored in a *MySQL* database. Pages are dynamically generated through a php3 interface to the database content. Users contribute images and descriptions. Contributed images are stored on the web server to avoid storing them in the database as BLOBs. All other information is stored in on the shared *MySQL* server. General database links ---------------------- * Database Jump Site (http://www.pcslink.com/~ej/dbweb.html) * Homepage of the webdb-l (Web Databases) mailing list. (http://black.hole-in-the.net/guy/webdb/) * Perl `DBI'/`DBD' modules homepage (http://www.symbolstone.org/technology/perl/DBI/index.html) * Cygwin tools (MySQL +Apache + PHP under Win32 (http://www-public.rz.uni-duesseldorf.de/~tolj) * dbasecentral.com; Development and distribution of powerful and easy-to-use database applications and systems. (http://dbasecentral.com/) * Tek-Tips Forums (http://www.Tek-Tips.com) Tek-Tips Forums are 800+ independent peer-to-peer non-commercial support forums for Computer Professionals. Features include automatic e-mail notification of responses, a links library, and member confidentiality guaranteed. There are also many web pages that use *MySQL*. *Note Users::. Send any additions to this list to . We now require that you show a *MySQL* logo somewhere (It is okay to have it on a "used tools" page or something similar) to be added. MySQL mailing lists and how to ask questions or report errors (bugs) ******************************************************************** The MySQL mailing lists ======================= To subscribe to the main *MySQL* mailing list, send a message to the electronic mail address . To unsubscribe from the main *MySQL* mailing list, send a message to the electronic mail address . Only the address to which you send your messages is significant. The subject line and the body of the message are ignored. If your reply address is not valid, you can specify your address explicitly. Adding a hyphen to the subscribe or unsubscribe command word, followed by your address with the `@' character in your address replaced by a `='. For example, to subscribe `john@host.domain', send a message to `mysql-subscribe-john=host.domain@lists.mysql.com'. Mail to or is handled automatically by the ezmlm mailing list processor. Information about ezmlm is available at the ezmlm Website (http://www.ezmlm.org). To post a message to the list itself, send your message to `mysql@lists.mysql.com'. However, please *do not* send mail about subscribing or unsubscribing to , since any mail sent to that address is distributed automatically to thousands of other users. Your local site may have many subscribers to . If so, it may have a local mailing list, so that messages sent from `lists.mysql.com' to your site are propagated to the local list. In such cases, please contact your system administrator to be added to or dropped from the local *MySQL* list. The following *MySQL* mailing lists exist: `announce' This is for announcement of new versions of *MySQL* and related programs. This is a low volume list that we think all *MySQL* users should be on. `mysql' The main list for general *MySQL* discussion. Please note that some topics are better discussed on the more-specialized lists. If you post to the wrong list, you may not get an answer! `mysql-digest' The `mysql' list in digest form. That means you get all individual messages, sent as one large mail message once a day. `java' Discussion about *MySQL* and Java. Mostly about the JDBC drivers. `java-digest' A digest version of the `java' list. `win32' All things concerning *MySQL* on Microsoft operating systems such as Windows NT. `win32-digest' A digest version of the `win32' list. `myodbc' All things concerning connecting to *MySQL* with ODBC. `myodbc-digest' A digest version of the `myodbc' list. `msql-mysql-modules' A list about the Perl support in *MySQL*. `msql-mysql-modules-digest' A digest version of the `msql-mysql-modules' list. `developer' A list for people who work on the *MySQL* code. `developer-digest' A digest version of the `developer' list. You subscribe or unsubscribe to all lists in the same way as described above. In your subscribe or unsubscribe message, just put the appropriate mailing list name rather than `mysql'. For example, to subscribe to or unsubscribe from the `myodbc' list, send a message to or . Asking questions or reporting bugs ================================== Before posting a bug report or question, please do the following: * Start by searching the *MySQL* online manual at: `http://www.mysql.com/Manual_chapter/manual_toc.html' We try to keep the manual up to date by updating it frequently with solutions to newly found problems! * Search the *MySQL* mailing list archives: `http://www.mysql.com/doc.html' * You can also use `http://www.mysql.com/search.html' to search all the web pages (including the manual) that are located at `http://www.mysql.com/'. If you can't find an answer in the manual or the archives, check with your local *MySQL* expert. If you still can't find an answer to your question, go ahead and read the next section about how to send mail to . How to report bugs or problems ============================== Writing a good bug report takes patience, but doing it right the first time saves time for us and for you. This section will help you write your report correctly so that you don't waste your time doing things that may not help us much or at all. We encourage everyone to use the `mysqlbug' script to generate a bug report (or a report about any problem), if possible. `mysqlbug' can be found in the `scripts' directory in the source distribution, or, for a binary distribution, in the `bin' directory under your *MySQL* installation directory. If you are unable to use `mysqlbug', you should still include all the necessary information listed in this section. The `mysqlbug' script helps you generate a report by determining much of the following information automatically, but if something important is missing, please include it with your message! Please read this section carefully and make sure that all the information described here is included in your report. Remember that it is possible to respond to a message containing too much information, but not to one containing too little. Often people omit facts because they think they know the cause of a problem and assume that some details don't matter. A good principle is: if you are in doubt about stating something, state it! It is a thousand times faster and less troublesome to write a couple of lines more in your report than to be forced to ask again and wait for the answer because you didn't include enough information the first time. The most common errors are that people don't indicate the version number of the *MySQL* distribution they are using, or don't indicate what platform they have *MySQL* installed on (including the platform version number). This is highly relevant information and in 99 cases out of 100 the bug report is useless without it! Very often we get questions like "Why doesn't this work for me?" and then we find that the feature requested wasn't implemented in that *MySQL* version, or that a bug described in a report has been fixed already in newer *MySQL* versions. Sometimes the error is platform dependent; in such cases, it is next to impossible to fix anything without knowing the operating system and the version number of the platform. Remember also to provide information about your compiler, if it is related to the problem. Often people find bugs in compilers and think the problem is *MySQL* related. Most compilers are under development all the time and become better version by version, too. To determine whether or not your problem depends on your compiler, we need to know what compiler is used. Note that every compiling problem should be regarded as a bug report and reported accordingly. It is most helpful when a good description of the problem is included in the bug report. That is, a good example of all the things you did that led to the problem and the problem itself exactly described. The best reports are those that include a full example showing how to reproduce the bug or problem. If a program produces an error message, it is very important to include the message in your report! If we try to search for something from the archives using programs, it is better that the error message reported exactly matches the one that the program produces. (Even the case sensitivity should be observed!) You should never try to remember what the error message was; instead, copy and paste the entire message into your report! Please include the following information in your report: * The version number of the *MySQL* distribution you are using (for example, *MySQL* 3.22.22). You can find out which version you are running by executing `mysqladmin version'. `mysqladmin' can be found in the `bin' directory under your *MySQL* installation directory. * The manufacturer and model of the machine you are working on. * The operating system name and version. For most operating systems, you can get this information by executing the Unix command `uname -a'. * Sometimes the amount of memory (real and virtual) is relevant. If in doubt, include these values. * If you are using a source distribution of *MySQL*, the name and version number of the compiler used is needed. If you have a binary distribution, the distribution name is needed. * If the problem occurs during compilation, include the exact error message(s) and also a few lines of context around the offending code in the file where the error occurred. * If any database table is related to the problem, include the output from `mysqldump --no-data db_name tbl_name1 tbl_name2 ...' This is very easy to do and is a powerful way to get information about any table in a database that will help us create a situation matching the one you have. * For speed-related bugs or problems with `SELECT' statements, you should always include the output of `EXPLAIN SELECT ...', and at least the number of rows that the `SELECT' statement produces. The more information you give about your situation, the more likely it is that someone can help you! For example, the following is an example of a very good bug report (it should of course be posted with the `mysqlbug' script): Example run under the `mysql' command line tool: mysql> SHOW VARIABLES; mysql> EXPLAIN SELECT ... mysql> FLUSH STATUS; mysql> SELECT ... mysql> SHOW STATUS; * If a bug or problem occurs while running *MySQL*, try to provide an input script that will reproduce the anomaly. This script should include any necessary source files. The more closely the script can reproduce your situation, the better. If you can't provide a script, you should at least include the output from `mysqladmin variables extended-status processlist' in your mail to provide some information of how your system is performing! * If you think that *MySQL* produces a strange result from a query, include not only the result, but also your opinion of what the result should be and an account describing the basis for your opinion. * When giving an example of the problem, it's better to use the variable names, table names, etc., that exist in your actual situation than to come up with new names. The problem could be related to the name of a variable, table, etc.! These cases are rare, perhaps, but it is better to be safe than sorry. After all, it should be easier for you to provide an example that uses your actual situation and it is by all means better for us. In case you have data you don't want to show to others, you can use `ftp' to transfer it to `ftp://www.mysql.com/pub/mysql/secret/'. If the data are really top secret and you don't want to show them even to us, then go ahead and provide an example using other names, but please regard this as the last choice. * Include all the options given to the relevant programs, if possible. For example, indicate the options that you use when you start the `mysqld' daemon and that you use to run any *MySQL* client programs. The options to programs like `mysqld' and `mysql', and to the `configure' script are often keys to answers and very relevant! It is never a bad idea to include them anyway! If you use any modules, such as Perl or PHP, please include the version number(s) of those as well. * If you can't produce a test case in a few rows, or if the test table is too big to be mailed to the mailing list (more than 10 rows), you should dump your tables using `mysqldump' and create a `README' file that describes your problem. Create a compressed archive of your files using `tar' and `gzip' or `zip', and use `ftp' to transfer the archive to `ftp://www.mysql.com/pub/mysql/secret/'. Then send a short description of the problem to . * If your question is related to the privilege system, please include the output of `mysqlaccess', the output of `mysqladmin reload' and all the error messages you get when trying to connect! When you test your privileges, you should first run `mysqlaccess'. After this, execute `mysqladmin reload version', and last you should try to connect with the program that gives you trouble. `mysqlaccess' can be found in the `bin' directory under your *MySQL* installation directory. * If you have a patch for a bug, that is good. But don't assume the patch is all we need or that we will use it even if you don't provide some necessary information such as test cases showing the bug that your patch fixes. We might find problems with your patch or we might not understand it at all; if so, we can't use it. If we can't verify exactly what the patch is meant for, we won't use it. Test cases will help us here. Show that the patch will handle all the situations that may occur. If we find a borderline case (even a rare one) where the patch won't work, the patch may be useless. * Guesses about what the bug is, why it occurs, or what it depends on, are usually wrong. Even we can't guess such things without first using a debugger to determine the real cause of a bug. * Indicate in your mail message that you have checked the reference manual and mail archive so others know that you have tried to solve your problem yourself. * If you get a `parse error', please check your syntax closely! If you can't find something wrong with it, it's extremely likely that your current version of *MySQL* doesn't support the query you are using. If you are using the current version and the manual at `http://www.mysql.com/doc.html' doesn't cover the syntax you are using, *MySQL* doesn't support your query. In this case, your only options are to implement the syntax yourself or email and ask for an offer to implement it! If the manual covers the syntax you are using, but you have an older version of *MySQL*, you should check the *MySQL* change history to see when the syntax was implemented. *Note News::. In this case, you have the option of upgrading to a newer version of *MySQL*. * If you have a problem such that your data appears corrupt or you get errors when you access some particular table, you should first check and then try repairing your tables with `isamchk'. *Note Maintenance::. * If you often get corrupted tables you should try to find out when and why this happens! In this case, the `mysql-data-directory/'hostname'.err' file may contain some information about what happened. Please include any relevant information from this file in your bug report! Normally `mysqld' should *NEVER* crash a table if nothing killed it in the middle of an update! If you can find the source of why `mysqld' dies, it's much easier for us to provide you with a fix for the problem! * If possible, download the most recent version of *MySQL* and check whether or not it solves your problem. All versions of *MySQL* are thoroughly tested and should work without problems! We believe in making everything as backward compatible as possible and you should be able to switch *MySQL* versions in minutes! *Note Which version::. If you are a support customer, please cross-post the bug report to for higher priority treatment, as well as to the appropriate mailing list to see if someone else has experienced (and perhaps solved) the problem. For information on reporting bugs in *MyODBC*, see *Note ODBC Problems::. For solutions to some common problems, see *Note Problems::. When answers are sent to you individually and not to the mailing list, it is considered good etiquette to summarize the answers and send the summary to the mailing list so that others may have the benefit of responses you received that helped you solve your problem! Guidelines for answering questions on the mailing list ====================================================== If you consider your answer to have broad interest, you may want to post it to the mailing list instead of replying directly to the individual who asked. Try to make your answer general enough that people other than the original poster may benefit from it. When you post to the list, please make sure that your answer is not a duplication of a previous answer. Try to summarize the essential part of the question in your reply; don't feel obliged to quote the entire original message. Please don't post mail messages from your browser with HTML mode turned on! Many users doesn't read mail with a browser! MySQL licensing and support *************************** This chapter describes *MySQL* licensing and support arrangements, including: * Our licensing policies for non-Microsoft and Microsoft operating systems * The copyrights under which *MySQL* is distributed (*note Copyright::.) * Sample situations illustrating when a license is required (*note Licensing examples::.) * Licensing and support costs (*note Cost::.), and support benefits (*note Support::.) MySQL licensing policy ====================== The formal terms of the license for non-Microsoft operating systems such as Unix or OS/2 are specified in *Note Public license::. Basically, our licensing policy is as follows: * For normal internal use, *MySQL* generally costs nothing. You do not have to pay us if you do not want to. * A license is required if: - You sell the *MySQL* server directly or as a part of another product or service - You charge for installing and maintaining a *MySQL* server at some client site - You include *MySQL* in a distribution that is non redistributable and you charge for some part of that distribution * For circumstances under which a *MySQL* license is required, you need a license per machine that runs the `mysqld' server. However, a multiple-CPU machine counts as a single machine, and there is no restriction on the number of *MySQL* servers that run on one machine, or on the number of clients concurrently connected to a server running on that machine! * You do not need a license to include client code in commercial programs. The client access part of *MySQL* is in the public domain. The `mysql' command line client includes code from the `readline' library that is under the GNU Public License. * For customers who have purchased 10 licenses or a high enough level of support, we provide additional functionality. Currently, this means we provide the `pack_isam' utility for creating fast compressed read-only databases. (The server includes support for reading such databases but not the packing tool used to create them.) If support agreements generate sufficient revenue, we will probably release this tool under the same license as the *MySQL* server. * If your use of *MySQL* does not require a license, but you like *MySQL* and want to encourage further development, you are certainly welcome to purchase a license anyway. * If you use *MySQL* in a commercial context such that you profit by its use, we ask that you further the development of *MySQL* by purchasing some level of support. We feel that if *MySQL* helps your business, it is reasonable to ask that you help *MySQL*. (Otherwise, if you ask us support questions, you are not only using for free something into which we've put a lot a work, you're asking us to provide free support, too.) For use under Microsoft operating systems (Win95/Win98/WinNT), you need a *MySQL* license after a trial period of 30 days, with the exception that licenses may be obtained upon request at no cost for educational use or for university- or government-sponsored research settings. *Note Win license::. A shareware version of *MySQL*-Win32 that you can try before buying is available at `http://www.mysql.com/mysql_w32.htmy'. After you have paid, you will get a password that will enable you to access the newest *MySQL*-Win32 version. If you have any questions as to whether or not a license is required for your particular use of *MySQL*, please contact us. *Note Contact information::. If you require a *MySQL* license, the easiest way to pay for it is to use the license form at TcX's secure server at `https://www.mysql.com/license.htmy'. Other forms of payment are discussed in *Note Payment information::. Copyrights used by MySQL ======================== There are several different copyrights on the *MySQL* distribution: 1. The *MySQL*-specific source needed to build the `mysqlclient' library and programs in the `client' directory is in the public domain. Each file that is in the public domain has a header which clearly states so. This includes everything in the `client' directory and some parts of the `mysys', `mystring' and `dbug' libraries. 2. Some small parts of the source (GNU `getopt') are covered by the "GNU LIBRARY LIBRARY GENERAL PUBLIC LICENSE". See the `mysys/COPYING.LIB' file. 3. Some small parts of the source (GNU `readline') are covered by the "GNU GENERAL PUBLIC LICENSE". See the `readline/COPYING' file. 4. Some parts of the source (the `regexp' library) are covered by a Berkeley style copyright. 5. The other source needed for the *MySQL* server on non-Microsoft platforms is covered by the "MySQL FREE PUBLIC LICENSE", which is based on the "Aladdin FREE PUBLIC LICENSE." *Note Public license::. When running *MySQL* on any Microsoft operating system, other licensing applies. The following points set forth the philosophy behind our copyright policy: * The SQL client library should be totally free so that it can be included in commercial products without limitations. * People who want free access to the software into which we have put a lot of work can have it, so long as they do not try to make money directly by distributing it for profit. * People who want the right to keep their own software proprietary, but also want the value from our work, can pay for the privilege. * That means normal in-house use is FREE. But if you use *MySQL* for something important to you, you may want to help further its development by purchasing a license or a support contract. *Note Support::. Possible future copyright changes --------------------------------- We may choose to distribute older versions of *MySQL* with the GPL in the future. However, these versions will be identified as *GNU MySQL*. Also, all copyright notices in the relevant files will be changed to the GPL. Distributing MySQL commercially =============================== This section is a clarification of the license terms that are set forth in the "MySQL FREE PUBLIC LICENSE" (FPL). *Note Public license::. *MySQL* may be *used* freely, including by commercial entities for evaluation or unsupported internal use. However, *distribution* for commercial purposes of *MySQL*, or anything containing or derived from *MySQL* in whole or in part, requires a written commercial license from TcX AB, the sole entity authorized to grant such licenses. You may not include *MySQL* "free" in a package containing anything for which a charge is being made, except as noted below. The intent of the exception provided in the second clause of the license is to allow commercial organizations operating an FTP server or a bulletin board to distribute *MySQL* freely from it, provided that: 1. The organization complies with the other provisions of the FPL, which include among other things a requirement to distribute the full source code of *MySQL* and of any derived work, and to distribute the FPL itself along with *MySQL*; 2. The only charge for downloading *MySQL* is a charge based on the distribution service and not one based on the content of the information being retrieved (i.e., the charge would be the same for retrieving a random collection of bits of the same size); 3. The server or BBS is accessible to the general public, i.e., the phone number or IP address is not kept secret, and anyone may obtain access to the information (possibly by paying a subscription or access fee that is not dependent on or related to purchasing anything else). If you want to distribute software in a commercial context that incorporates *MySQL* and you do *not* want to meet these conditions, you should contact TcX AB to find out about commercial licensing, which involves a payment. The only ways you legally can distribute *MySQL* or anything containing *MySQL* are by distributing *MySQL* under the requirements of the FPL, or by getting a commercial license from TcX AB. Example licensing situations ============================ This section describes some situations illustrating whether or not you must license the *MySQL* server. Generally these examples involve providing *MySQL* as part of a product or service that you are selling to a customer, or requiring that *MySQL* be used in conjunction with your product. In such cases, it is your responsibility to obtain a license for the customer if one is necessary. (This requirement is waived if your customer already has a *MySQL* license. But the seller must send customer information and the license number to TcX, and the license must be a full license, not an OEM license.) Note that a single *MySQL* license covers any number of CPUs/users/customers/`mysqld' servers on a machine! Selling products that use MySQL ------------------------------- To determine whether or not you need a *MySQL* license when selling your application, you should ask whether the proper functioning of your application is contingent on the use of *MySQL* and whether you include *MySQL* with your product. There are several cases to consider: * Does your application require *MySQL* to function properly? If your product requires *MySQL*, you need a license for any machine that runs the `mysqld' server. For example, if you've designed your application around *MySQL*, then you've really made a commercial product that requires the engine, so you need a license. If your application does not require *MySQL*, you need not obtain a license. For example, if *MySQL* just added some new optional features to your product (such as adding logging to a database if *MySQL* is used rather than logging to a text file), it should fall within normal use, and a license would not be required. In other words, you need a license if you sell a product designed specifically for use with *MySQL* or that requires the *MySQL* server to function at all. This is true whether or not you provide *MySQL* for your client as part of your product distribution. It also depends on what you're doing for the client. Do you plan to provide your client with detailed instructions on installing *MySQL* with your software? Then your product may be contingent on the use of *MySQL*; if so, you need to buy a license. If you are simply tying into a database that you expect already to have been installed by the time your software is purchased, then you probably don't need a license. * Do you include *MySQL* in a distribution and charge for that distribution? If you include *MySQL* with a distribution that you sell to customers, you will need a license for any machine that runs the `mysqld' server, because in this case you are selling a system that includes *MySQL*. This is true whether the use of *MySQL* with your product is required or optional. * Do you neither require for your product nor include *MySQL* with it? Suppose you want to sell a product that is designed generally to use "some database" and that can be configured to use any of several supported alternative database systems (*MySQL*, PostgreSQL, or something else). That is, your product does not not require *MySQL*, but can support any database with a base level of functionality, and you don't rely on anything that only *MySQL* supports. Does one of you owe us money if your customer actually does choose to use *MySQL*? In this case, if you don't provide, obtain or set up *MySQL* for the customer should the customer decide to use it, neither of you need a license. If you do perform that service, see *Note *MySQL* services: MySQL services. Selling MySQL-related services ------------------------------ If you perform *MySQL* installation on a client's machine and any money changes hands for the service (directly or indirectly), then you must buy a *MySQL* license. If you sell an application for which *MySQL* is not strictly required but can be used, a license may be indicated, depending on how *MySQL* is set up. Suppose your product neither requires *MySQL* nor includes it in your product distribution, but can be configured to use *MySQL* for those customers who so desire. (This would be the case, for example, if your product can use any of a number of database engines.) If the customer obtains and installs *MySQL*, no license is needed. If you perform that service for your customer, then a license is needed because then you are selling a service that includes *MySQL*. ISP MySQL services ------------------ Internet Service Providers (ISPs) often host *MySQL* servers for their customers. If you are an ISP that allows customers to install and administer *MySQL* for themselves on your machine with no assistance from you, neither you nor your customer need a *MySQL* license. If you charge for *MySQL* installation and administrative support as part of your customer service, then you need a license because you are selling a service that includes *MySQL*. Running a web server using MySQL -------------------------------- If you use *MySQL* in conjunction with a web server, you don't have to pay for a license. This is true even if you run a commercial web server that uses *MySQL*, since you are not selling *MySQL* itself. However, in this case we would like you to purchase *MySQL* support, because *MySQL* is helping your enterprise. MySQL licensing and support costs ================================= Our current license prices are shown below. All prices are in US Dollars. If you pay by credit card, the currency is EURO (European Union Euro) so the prices will differ slightly. *Number of *Price per *Total* licenses* copy* 1 US $200 US $200 10 pack US $150 US $1500 50 pack US $120 US $6000 For high volume (OEM) purchases, the following prices apply: *Number of *Price per *Minimum at one time* *Minimum payment* licenses* copy* 100-999 US $40 100 US $4000 1000-2499 US $25 200 US $5000 2500-4999 US $20 400 US $8000 For OEM purchases, you must act as the middle-man for eventual problems or extension requests from your users. We also require that OEM customers have at least an extended email support contract. If you have a low-margin high-volume product, you can always talk to us about other terms (for example, a percent of the sale price). If you do, please be informative about your product, pricing, market and any other information that may be relevant. After buying 10 *MySQL* licenses, you will get a personal copy of the `pack_isam' utility. You are not allowed to redistribute this utility but you can distribute tables packed with it. A full-price license is not a support agreement and includes very minimal support. This means that we try to answer any relevant question. If the answer is in the documentation, we will direct you to the appropriate section. If you have not purchased a license or support, we probably will not answer at all. If you discover what we consider a real bug, we are likely to fix it in any case. But if you pay for support we will notify you about the fix status instead of just fixing it in a later release. More comprehensive support is sold separately. Descriptions of what each level of support includes are given in *Note Support::. Costs for the various types of commercial support are shown below. Support level prices are in EURO (European Union Euro). One EURO is about 1.17 USD. *Type of support* *Cost per year* Basic email support EURO 170 Extended email EURO 1000 support Login support EURO 2000 Extended login EURO 5000 support You may upgrade from any lower level of support to a higher level of support for the difference between the prices of the two support levels. Payment information ------------------- Currently we can take SWIFT payments, cheques or credit cards. Payment should be made to: Postgirot Bank AB 105 06 STOCKHOLM, SWEDEN TCX DataKonsult AB BOX 6434 11382 STOCKHOLM, SWEDEN SWIFT address: PGSI SESS Account number: 96 77 06 - 3 Specify: license and/or support and your name and email address. In Europe and Japan you can use EuroGiro (that should be less expensive) to the same account. If you want to pay by cheque, make it payable to "Monty Program KB" and mail it to the address below: TCX DataKonsult AB BOX 6434, Torsgatan 21 11382 STOCKHOLM, SWEDEN If you want to pay by credit card over the Internet, you can use TcX's secure license form (https://www.mysql.com/license.htmy). You can also print a copy of the license form, fill it in and send it by fax to: +46-8-729 69 05 If you want us to bill you, you can use the license form and write "bill us" in the comment field. You can also mail a message to (*not* !) with your company information and ask us to bill you. Contact information ------------------- For commercial licensing, or if you have any questions about any of the information in this section, please contact the *MySQL* licensing team. The much preferred method is by E-Mail to . Fax is also possible but handling of these may take much longer (Fax +46-8-729 69 05). David Axmark Detron HB Kungsgatan 65 B 753 21 UPPSALA SWEDEN Voice Phone +46-18-10 22 80 (Timezone GMT+1. Swedish and English spoken) Types of commercial support =========================== Basic email support ------------------- Basic email support is a very inexpensive support option and should be thought of more as a way to support our development of *MySQL* than as a real support option. At this support level, the *MySQL* mailing lists are the preferred means of communication. Questions normally should be mailed to the primary mailing list () or one of the other regular lists (for example, for Windows-related *MySQL* questions), as someone else already may have experienced and solved the problem you have. *Note Asking questions::. However, by purchasing basic email support, you also have access to the support address , which is not available as part of the minimal support that you get by purchasing a *MySQL* license. This means that for especially critical questions, you can cross-post your message to . (If the message contains sensitive data, you should post only to .) *REMEMBER!* to ALWAYS include your registration number and expiration date when you send a message to . Basic email support includes the following types of service: * If your question is already answered in the manual, we will inform you of the correct section in which you can find the answer. If the answer is not in the manual, we will point you in the right direction to solve your problem. * We guarantee a timely answer for your email messages. We can't guarantee that we can solve any problem, but at least you will receive an answer if we can contact you by email. * We will help with unexpected problems when you install *MySQL* from a binary distribution on supported platforms. This level of support does not cover installing *MySQL* from a source distribution. "Supported" platforms are those for which *MySQL* is known to work. *Note Which OS::. * We will help you with bugs and missing features. Any bugs that are found are fixed for the next *MySQL* release. If the bug is critical for you, we will mail you a patch for it as soon the bug is fixed. Critical bugs always have the highest priority for us, to ensure that they are fixed as soon as possible. * Your suggestions for the further development of *MySQL* will be taken into consideration. By taking email support you have already helped the further development of *MySQL*. If you want to have more input, upgrade to a higher level of support. * If you want us to help optimize your system, you must upgrade to a higher level of support. Extended email support ---------------------- Extended email support includes everything in basic email support with these additions: * Your email will be dealt with before mail from basic email support users and non-registered users. * Your suggestions for the further development of *MySQL* will receive strong consideration. Simple extensions that suit the basic goals of *MySQL* are implemented in a matter of days. By taking extended email support you have already helped the further development of *MySQL*. * We include a binary version of the `pack_isam' packing tool for creating fast compressed read-only databases (it does not support `BLOB' or `TEXT' types yet). The current server includes support for reading such databases but not the packing tool used to create them. * Typical questions that are covered by extended email support are: - We will answer and (within reason) solve questions that relate to possible bugs in *MySQL*. As soon as the bug is found and corrected, we will mail a patch for it. - We will help with unexpected problems when you install *MySQL* from a source or binary distribution on supported platforms. - We will answer questions about missing features and offer hints how to work around them. - We will provide hints on optimizing `mysqld' for your situation. * You are allowed to influence the priority of items on the *MySQL* TODO. This will ensure that the features you really need will be implemented sooner than they might be otherwise. Login support ------------- Login support includes everything in extended email support with these additions: * Your email will be dealt with even before mail from extended email support users. * Your suggestions for the further development of *MySQL* will be taken into very high consideration. Realistic extensions that can be implemented in a couple of hours and that suit the basic goals of *MySQL* will be implemented as soon as possible. * If you have a very specific problem, we can try to log in on your system to solve the problem "in place." * Like any database vendor, we can't guarantee that we can rescue any data from crashed tables, but if the worst happens we will help you rescue as much as possible. *MySQL* has proven itself very reliable, but anything is possible due to circumstances beyond our control (for example, if your system crashes or someone kills the server by executing a `kill -9' command). * We will provide hints on optimizing your system and your queries. * You are allowed to call a *MySQL* developer (in moderation) and discuss your *MySQL*-related problems. Extended login support ---------------------- Extended login support includes everything in login support with these additions: * Your email has the highest possible priority. * We will actively examine your system and help you optimize it and your queries. We may also optimize and/or extend *MySQL* to better suit your needs. * You may also request special extensions just for you. For example: mysql> select MY_CALCULATION(col_name1,col_name2) from tbl_name; * We will provide a binary distribution of all important *MySQL* releases for your system, as long as we can get an account on a similar system. In the worst case, we may require access to your system to be able to create a binary distribution. * If you can provide accommodations and pay for traveler fares, you can even get a *MySQL* developer to visit you and offer you help with your troubles. Extended login support entitles you to one personal encounter per year, but we are as always very flexible towards our customers! Installing MySQL **************** This chapter describes how to obtain and install *MySQL*: * For a list of sites from which you can obtain *MySQL*, see *Note Getting *MySQL*: Getting MySQL. * To see which platforms are supported, see *Note Which OS::. * Several versions of *MySQL* are available, in both binary and source distributions. To determine which version and type of distribution you should use, see *Note Many versions::. * Installation instructions for binary and source distributions are described in *Note Installing binary::, and *Note Installing source::. Each set of instructions includes a section on system-specific problems you may run into. * For post-installation procedures, see *Note Post-installation::. These procedures apply whether you install *MySQL* using a binary or source distribution. How to get MySQL ================ Check the *MySQL* home page (http://www.mysql.com/) for information about the current version and for downloading instructions. However, the Internet connection at TcX is not so fast; we would *prefer* that you do the actual downloading from one of the mirror sites listed below. Please report bad or out of date mirrors to . *Europe:* * Austria [Univ. of Technology/Vienna] WWW (http://gd.tuwien.ac.at/db/mysql/) FTP (ftp://gd.tuwien.ac.at/db/mysql/) * Bulgaria [Naturella] FTP (ftp://ftp.ntrl.net/pub/mirror/mysql) * Croatia [HULK] WWW (http://ftp.linux.hr/pub/mysql/) FTP (ftp://ftp.linux.hr/pub/mysql/) * Czech Republic [Masaryk University in Brno] WWW (http://mysql.linux.cz/index.html) FTP (ftp://ftp.fi.muni.cz/pub/mysql/) * Czech Republic [www.sopik.cz] WWW (http://www.mysql.cz/) * Denmark [Ake] WWW (http://mysql.ake.dk) * Denmark [SunSITE] WWW (http://SunSITE.auc.dk/mysql/) FTP (ftp://SunSITE.auc.dk/pub/databases/mysql/) * Estonia [OKinteractive] WWW (http://mysql.mirror.ok.ee) * France [minet] WWW (http://www.minet.net/devel/mysql/) * Finland [EUnet] WWW (http://mysql.eunet.fi/) * Finland [clinet] FTP (ftp://ftp.clinet.fi/mirrors/ftp.mysql.org/pub/mysql/) * Germany [Bonn University, Bonn] WWW (http://www.wipol.uni-bonn.de/MySQL//) FTP (ftp://ftp.wipol.uni-bonn.de/pub/mirror/MySQL/) * Germany [Wolfenbuettel] WWW (http://www.fh-wolfenbuettel.de/ftp/pub/database/mysql/) FTP (ftp://ftp.fh-wolfenbuettel.de/pub/database/mysql/) * Germany [Staufen] WWW (http://mysql.staufen.de/) * Germany [Cable & Wireless] FTP (ftp://ftp.ecrc.net/pub/database/mysql/) * Greece [NTUA, Athens] WWW (http://www.ntua.gr/mysql/) FTP (ftp://ftp.ntua.gr/pub/databases/mysql/) * Italy [Teta Srl] WWW (http://www.teta.it/mysql/) * Poland [Sunsite] WWW (http://sunsite.icm.edu.pl/mysql/) FTP (ftp://sunsite.icm.edu.pl/pub/unix/mysql/) * Portugal [lerianet] WWW (http://mysql.leirianet.pt) FTP (ftp://ftp.leirianet.pt/pub/mysql/) * Russia [DirectNet] WWW (http://mysql.directnet.ru) * Russia [IZHCOM] WWW (http://mysql.udm.net/) FTP (ftp://ftp.izhcom.ru/pub/mysql/) * Russia [Scientific Center/Chernogolovka] FTP (ftp://ftp.chg.ru/pub/databases/mysql/) * Romania [Timisoara] WWW (http://www.dnttm.ro/mysql) FTP (ftp://ftp.dnttm.ro/pub/mysql) * Romania [Bucharest] WWW (http://www.lbi.ro/MySQL) FTP (ftp://ftp.lbi.ro/mirrors/ftp.tcx.se) * Spain [MasterD] WWW (http://mysql.masterd.es) * Sweden [Sunet] WWW (http://ftp.sunet.se/pub/unix/databases/relational/mysql/) FTP (ftp://ftp.sunet.se/pub/unix/databases/relational/mysql/) * Switzerland [Sunsite] WWW (http://sunsite.cnlab-switch.ch/ftp/mirror/mysql/) FTP (ftp://sunsite.cnlab-switch.ch/mirror/mysql/) * UK [Omnipotent/UK] WWW (http://mysql.omnipotent.net/) FTP (ftp://mysql.omnipotent.net/) * UK [PLiG/UK] WWW (http://ftp.plig.org/pub/mysql/) FTP (ftp://ftp.plig.org/pub/mysql/) * UK [SunSITE] WWW (http://sunsite.org.uk/packages/mysql/) FTP (ftp://sunsite.org.uk/packages/mysql/) * Ukraine [PACO] WWW (http://mysql.paco.net.ua) FTP (ftp://mysql.paco.net.ua/) *North America:* * Canada [Tryc] WWW (http://web.tryc.on.ca/mysql/) * Canada [Cyberus] WWW (http://mysql.cyberus.ca/) FTP (ftp://mysql.cyberus.ca/) * USA [Hurricane Electric/San Jose] WWW (http://mysql.he.net) * USA [Netcasting/West Coast] FTP (ftp://ftp.netcasting.net/pub/mysql/) * USA [Circle Net/North Carolina] WWW (http://www.mysql.net) * USA [Gina net/Florida] WWW (http://www.gina.net/mysql/) * USA [pingzero/Los Angeles] WWW (http://mysql.pingzero.net/) * USA [Wisconsin University/Wisconsin] WWW (http://mirror.sit.wisc.edu/mysql/) FTP (ftp://mirror.sit.wisc.edu/mirrors/mysql/) * USA [DIGEX] FTP (ftp://ftp.digex.net/pub/packages/database/mysql/) *South America:* * Brazil [Matrix] WWW (http://mysql.matrix.com.br) * Chile [Vision] WWW (http://mysql.vision.cl/) *Asia:* * China [Freecode] WWW (http://www.freecode.com.cn/mirror/mysql/) * Korea [KREONet] WWW (http://linux.kreonet.re.kr/mysql/) * Japan [Soft Agency] WWW (http://www.softagency.co.jp/MySQL) * Japan [Nagoya Syouka University] WWW (http://mirror.nucba.ac.jp/mirror/mysql) FTP (ftp://mirror.nucba.ac.jp/mirror/mysql) * Singapore [HJC] WWW (http://mysql.hjc.edu.sg) FTP (ftp://ftp.hjc.edu.sg/mysql) * Taiwan [HT] WWW (http://mysql.ht.net.tw) *Australia:* * Australia [AARNet/Queensland] WWW (http://mirror.aarnet.edu.au/mysql) FTP (ftp://mirror.aarnet.edu.au/pub/mysql) * Australia [Tas] WWW (http://ftp.tas.gov.au/mysql) FTP (ftp://ftp.tas.gov.au/pub/mysql) * Australia [Blue Planet/Melbourne] WWW (http://mysql.bluep.com/) * Australia [ITworks Consulting/Victoria] WWW (http://mysql.itworks.com.au) *Africa:* * South-Africa [Mweb/] WWW (http://www.mysql.mweb.co.za) * South-Africa [The Internet Solution/Johannesburg] FTP (ftp://ftp.is.co.za/linux/mysql/) Operating systems supported by MySQL ==================================== We use GNU Autoconf so it is possible to port *MySQL* to all modern systems with working Posix threads and a C++ compiler. (To compile only the client code, a C++ compiler is required but not threads.) We use and develop the software ourselves primarily on Sun Solaris (versions 2.5 & 2.6) and to a lesser extent on RedHat Linux 5.0. *MySQL* has been reported to compile sucessfully on the following operating system/thread package combinations. Note that for many operating systems, the native thread support works only in the latest versions. * AIX 4.x with native threads * BSDI 2.x with the included MIT-pthreads package * BSDI 3.0, 3.1 and 4.x with native threads * DEC UNIX 4.x with native threads * FreeBSD 2.x with the included MIT-pthreads package * FreeBSD 3.x with native threads * HP-UX 10.20 with the included MIT-pthreads package * HP-UX 11.x with the native threads. * Linux 2.0+ with LinuxThreads 0.7.1 or `glibc' 2.0.7 * NetBSD 1.3/1.4 Intel and NetBSD 1.3 Alpha (Requires GNU make) * OpenBSD 2.x with the included MIT-pthreads package * OS/2 Warp 3, FixPack 29 and OS/2 Warp 4, FixPack 4 * SGI Irix 6.x with native threads * Solaris 2.5, 2.6 and 2.7 with native threads on SPARC and x86 * SunOS 4.x with the included MIT-pthreads package * SCO OpenServer with a recent port of the FSU Pthreads package * SCO UnixWare 7.0.1 * Tru64 Unix * Win95, Win98 and NT (the newest version is currently available only for users with a *MySQL* license or *MySQL* email support). For those who wish to test before they buy, we have released *MySQL* 3.21.29 (http://www.mysql.com/mysql_w32.htmy) (an older version) as shareware. Which MySQL version to use ========================== The first decision to make is whether you want to use the latest development release or the last stable release: * Normally, if you are beginning to use *MySQL* for the first time or trying to port it to some system for which there is no binary distribution, we recommend going with the development release (currently 3.22.x). This is because there are usually no really serious bugs in the development release, and you can easily test it on your machine with the `crash-me' and benchmark tests. *Note Benchmarks::. * Otherwise, if you are running an old system and want to upgrade, but don't want to take chances with 3.22, you should upgrade to 3.21.33. We have tried to fix only fatal bugs and make small, relatively safe changes to that version. The second decision to make is whether you want to use a source distribution or a binary distribution: * If you want to run *MySQL* on a platform for which a current binary distribution exists, use that. Generally, it will be easier to install than a source distribution. * If you want to read (and/or modify) the C and C++ code that makes up *MySQL*, you should get a source distribution. The source code is always the ultimate manual. Source distributions also contain more tests and examples than binary distributions. The *MySQL* naming scheme uses release numbers that consist of three numbers and a suffix. For example, a release name like `mysql-3.21.17-beta' is interpreted like this: * The first number (`3') describes the file format. All version 3 releases have the same file format. When a version 4 appears, every table will have to be converted to the new format (nice tools for this will be included, of course). * The second number (`21') is the release level. Normally there are two to choose from. One is the release/stable branch (currently `21') and the other is the development branch (currently `22') . Normally both are stable, but the development version may have quirks, missing documentation on new features or may fail to compile on some systems. * The third number (`17') is the version number within the release level. This is incremented for each new distribution. Usually you want the latest version for the release level you have choosen. * The suffix (`beta') indicates the stability level of the release. The possible suffixes are: - `alpha' indicates that the release contains some large section of new code that hasn't been 100% tested. Known bugs (usually there are none) should be documented in the News section. *Note News::. There are also new commands and extensions in most alpha releases. - `beta' means that all new code has been tested. No major new features were added. There should be no known bugs. - `gamma' is a beta that has been around a while and seems to work fine. This is what many other companies call a release. - If there is no suffix, it means that the version has been run for a while at many different sites with no reports of bugs other than platform-specific bugs. This is what we call a stable release. All versions of *MySQL* are run through our standard tests and benchmarks to ensure that they are relatively safe to use. Since the standard tests are extended over time to check for all previously found bugs, the test suite keeps getting better. Note that all releases have been tested at least with: An internal test suite This is part of a production system for a customer. It has many tables with hundreds of megabytes of data. The *MySQL* benchmark suite This runs a range of common queries. It is also a test to see whether the latest batch of optimizations actually made the code faster. *Note Benchmarks::. The `crash-me' test This tries to determine what features the database supports and what its capabilities and limitations are. *Note Benchmarks::. Another test is that we use the newest *MySQL* version in our internal production environment, on at least one machine. We have more than 100 gigabytes of data to work with. How and when updates are released ================================= *MySQL* is evolving quite rapidly here at TcX and we want to share this with other *MySQL* users. We try to make a release when we have very useful features that others seem to have a need for. We also try to help out users who request features that are easy to implement. We also take note of what our licensed users want to have and we especially take note of what our extended email supported customers want and try to help them out. No one has to download a new release. The News section will tell you if the new release has something you really want. *Note News::. We use the following policy when updating *MySQL*: * For each minor update, the last number in the version string is incremented. When there are major new features or minor incompatibilities with previous versions, the second number in the version string is incremented. When the file format changes, the first number is increased. * Stable tested releases are meant to appear about 1-2 times a year, but if small bugs are found, a release with only bug-fixes will be released. * Working releases are meant to appear about every 1-8 weeks. * Binary distributions for some platforms will be made by us for major releases. Other people may make binary distributions for other systems but probably less frequently. * We usually make patches available as soon as we have located and fixed small bugs. * For non-critical but annoying bugs, we will make patches available if they are sent to us. Otherwise we will combine many of them into a larger patch. * If there is, by any chance, a fatal bug in a release we will make a new release as soon as possible. We would like other companies to do this, too. :) The current stable release is 3.22; We have already moved active development to 3.23. Bugs will still be fixed in the stable version. We don't believe in a complete freeze, as this also leaves out bug fixes and things that "must be done". "Somewhat frozen" means that we may add small things that "almost surely will not affect anything that's already working". Installation layouts ==================== This section describes the default layout of the directories created by installing binary and source distributions. A binary distribution is installed by unpacking it at the installation location you choose (typically `/usr/local/mysql') and creates the following directories in that location: *Directory* *Contents of directory* `bin' Client programs and the `mysqld' server `data' Log files, databases `include' Include (header) files `lib' Libraries `scripts' `mysql_install_db' `share/mysql' Error message files `sql-bench' Benchmarks A source distribution is installed after you configure and compile it. By default, the installation step installs files under `/usr/local', in the following subdirectories: *Directory* *Contents of directory* `bin' Client programs and scripts `include/mysql' Include (header) files `info' Documentation in Info format `lib/mysql' Libraries `libexec' The `mysqld' server `share/mysql' Error message files `sql-bench' Benchmarks and `crash-me' test `var' Databases and log files. Within an installation directory, the layout of a source installation differs from that of a binary installation in the following ways: * The `mysqld' server is installed in the `libexec' directory rather than in the `bin' directory. * The data directory is `var' rather than `data'. * `mysql_install_db' is installed in the `/usr/local/bin' directory rather than in `/usr/local/mysql/scripts'. * The header file and library directories are `include/mysql' and `lib/mysql' rather than `include' and `lib'. Installing a MySQL binary distribution ====================================== You need the following tools to install a *MySQL* binary distribution: * GNU `gunzip' to uncompress the distribution. * A reasonable `tar' to unpack the distribution. GNU `tar' is known to work. An alternative installation method under Linux is to use RPM (RedHat Package Manager) distributions. *Note Linux-RPM::. If you run into problems, *PLEASE ALWAYS USE* `mysqlbug' when posting questions to . Even if the problem isn't a bug, `mysqlbug' gathers system information that will help others solve your problem. By not using `mysqlbug', you lessen the likelihood of getting a solution to your problem! You will find `mysqlbug' in the `bin' directory after you unpack the distribution. *Note Bug reports::. The basic commands you must execute to install and use a *MySQL* binary distribution are: shell> gunzip < mysql-VERSION-OS.tar.gz | tar xvf - shell> ln -s mysql-VERSION-OS mysql shell> cd mysql shell> scripts/mysql_install_db shell> bin/safe_mysqld & You can add new users using the `bin/mysql_setpermission' script if you install the `DBI' and `Msql-Mysql-modules' Perl modules. Here follows a more detailed description: To install a binary distribution, follow the steps below, then proceed to *Note Post-installation::, for post-installation setup and testing: 1. Pick the directory under which you want to unpack the distribution, and move into it. In the example below, we unpack the distribution under `/usr/local' and create a directory `/usr/local/mysql' into which *MySQL* is installed. (The following instructions therefore assume you have permission to create files in `/usr/local'. If that directory is protected, you will need to perform the installation as `root'.) 2. Obtain a distribution file from one of the sites listed in *Note Getting *MySQL*: Getting MySQL. *MySQL* binary distributions are provided as compressed `tar' archives and have names like `mysql-VERSION-OS.tar.gz', where `VERSION' is a number (e.g., `3.21.15'), and `OS' indicates the type of operating system for which the distribution is intended (e.g., `pc-linux-gnu-i586'). 3. Unpack the distribution and create the installation directory: shell> gunzip < mysql-VERSION-OS.tar.gz | tar xvf - shell> ln -s mysql-VERSION-OS mysql The first command creates a directory named `mysql-VERSION-OS'. The second command makes a symbolic link to that directory. This lets you refer more easily to the installation directory as `/usr/local/mysql'. 4. Change into the installation directory: shell> cd mysql You will find several files and subdirectories in the `mysql' directory. The most important for installation purposes are the `bin' and `scripts' subdirectories. `bin' This directory contains client programs and the server You should add the full pathname of this directory to your `PATH' environment variable so that your shell finds the *MySQL* programs properly. `scripts' This directory contains the `mysql_install_db' script used to initialize the server access permissions. 5. If you would like to use `mysqlaccess' and have the *MySQL* distribution in some nonstandard place, you must change the location where `mysqlaccess' expects to find the `mysql' client. Edit the `bin/mysqlaccess' script at approximately line 18. Search for a line that looks like this: $MYSQL = '/usr/local/bin/mysql'; # path to mysql executable Change the path to reflect the location where `mysql' actually is stored on your system. If you do not do this, you will get a `broken pipe' error when you run `mysqlaccess'. 6. Create the *MySQL* grant tables (necessary only if you haven't installed *MySQL* before): shell> scripts/mysql_install_db Note that *MySQL* versions older than 3.22.10 started the *MySQL* server when you run `mysql_install_db'. This is no longer true! 7. If you want to install support for the Perl `DBI'/`DBD' interface, see *Note Perl support::. 8. If you would like *MySQL* to start automatically when you boot your machine, you can copy `support-files/mysql.server' to the location where your system has its startup files. More information can be found in the `support-files/mysql.server' script itself, and in *Note Automatic start::. After everything has been unpacked and installed, you should initialize and test your distribution. You can start the *MySQL* server with the following command: shell> bin/safe_mysqld & *Note Post-installation::. Linux RPM notes --------------- The recommended way to install *MySQL* on Linux is by using an RPM file. The *MySQL* RPMs are currently being built on a RedHat 5.2 system but should work on other versions of Linux that support `rpm' and use `glibc'. If you have problems with an RPM file, for example `Sorry, the host 'xxxx' could not be looked up', see *Note Binary notes-Linux::. The RPM files you may want to use are: * `MySQL-VERSION.i386.rpm' The *MySQL* server. You will need this unless you only want to connect to another *MySQL* server running on another machine. * `MySQL-client-VERSION.i386.rpm' The standard *MySQL* client programs. You probably always want to install this package. * `MySQL-bench-VERSION.i386.rpm' Tests and benchmarks. Requires Perl and msql-mysql-modules RPMs. * `MySQL-devel-VERSION.i386.rpm' Libraries and include files needed if you want to compile other *MySQL* clients, such as the Perl modules. * `MySQL-VERSION.src.rpm' This contains the source code for all of the above packages. It can also be used to try to build RPMs for other architectures (for example, Alpha or SPARC). To see all files in an RPM package: shell> rpm -qpl MySQL-VERSION.i386.rpm To perform a standard minimal installation, run this command: shell> rpm -i MySQL-VERSION.i386.rpm MySQL-client-VERSION.i386.rpm To install just the client package: shell> rpm -i MySQL-client-VERSION.i386.rpm The RPM places data in `/var/lib/mysql'. The RPM also creates the appropriate entries in `/sbin/rc.d/' to start the server automatically at boot time. (This means that if you have performed a previous installation, you may want to make a copy of your previously-installed *MySQL* startup file if you made any changes to it, so you don't lose your changes.) After installing the RPM file(s), go to the binary install section and use the instructions there, starting from the step that creates the *MySQL* grant tables. *Note Installing binary::. Building client programs ------------------------ If you compile *MySQL* clients that you've written yourself or that you obtain from a third party, they must be linked using the `-lmysqlclient' option on the link command. You may also need to specify a `-L' option to tell the linker where to find the library. For example, if the library is installed in `/usr/local/mysql/lib', use `-L/usr/local/mysql/lib -lmysqlclient' on the link command. For clients that use *MySQL* header files, you may need to specify a `-I' option when you compile them (for example, `-I/usr/local/mysql/include'), so the compiler can find the header files. System-specific issues ---------------------- The following sections indicate some of the issues that have been observed to occur on particular systems when installing *MySQL* from a binary distribution. Linux notes ........... *MySQL* needs at least Linux 2.0. The binary release is linked with `-static', which means you not normally need not worry about which version of the system libraries you have. You need not install LinuxThreads, either. A program linked with `-static' is slightly bigger than a dynamically-linked program but also slightly faster (3-5%). One problem however is that you can't use user definable functions (UDFs) with a statically-linked program. If you are going to write or use UDF functions (this is something only for C or C++ programmers) you must compile *MySQL* yourself, using dynamic linking. If you are using a `libc'-based system (instead of a `glibc2' system), you will probably get some problems with hostname resolving and getpwnam() with the binary release. (This is because `glibc' unfortunately depends on some external libraries to resolve hostnames and getwpent() , even when compiled with `-static'). In this case you probably get the following error message when you run `mysql_install_db': Sorry, the host 'xxxx' could not be looked up or the following error when you try to run mysqld with the `--user' option: getpwnam: No such file or directory You can solve this problem one of the following ways: * Get a *MySQL* source distribution (an RPM or the `tar' distribution) and install this instead. * Execute `mysql_install_db --force'; This will not execute the `resolveip' test in `mysql_install_db'. The downside is that you can't use host names in the grant tables; you must use IP numbers instead (except for `localhost'). If you are using an old *MySQL* release that doesn't support `--force' you have to remove the `resolveip' test in `mysql_install' with an editor. * Start mysqld with `su' instead of using `--user'. The Linux-Intel binary and RPM releases of *MySQL* are configured for the highest possible speed. We are always trying to use the fastest stable compiler available. *MySQL* Perl support requires Perl 5.004_03 or newer. HP-UX notes ........... The binary distribution of *MySQL* for HP-UX is distributed as an HP depot file and as a tar file. To use the depot file you must be running at least HP-UX 10.x to have access to HP's software depot tools. The HP version of *MySQL* was compiled on an HP 9000/8xx server under HP-UX 10.20, and uses MIT-pthreads. It is known to work well under this configuration. *MySQL* 3.22.26 and newer can also be built with HP's native thread package. Other configurations that may work: * HP 9000/7xx running HP-UX 10.20+ * HP 9000/8xx running HP-UX 10.30 The following configurations almost definitely won't work: * HP 9000/7xx or 8xx running HP-UX 10.x where x < 2 * HP 9000/7xx or 8xx running HP-UX 9.x To install the distribution, use one of the commands below, where `/path/to/depot' is the full pathname of the depot file: * To install everything, including the server, client and development tools: shell> /usr/sbin/swinstall -s /path/to/depot mysql.full * To install only the server: shell> /usr/sbin/swinstall -s /path/to/depot mysql.server * To install only the client package: shell> /usr/sbin/swinstall -s /path/to/depot mysql.client * To install only the development tools: shell> /usr/sbin/swinstall -s /path/to/depot mysql.developer The depot places binaries and libraries in `/opt/mysql' and data in `/var/opt/mysql'. The depot also creates the appropriate entries in `/sbin/init.d' and `/sbin/rc2.d' to start the server automatically at boot time. Obviously, this entails being `root' to install. To install the HP-UX tar distribution, you must have a copy of GNU `tar'. Installing a MySQL source distribution ====================================== You need the following tools to build and install *MySQL* from source: * GNU `gunzip' to uncompress the distribution. * A reasonable `tar' to unpack the distribution. GNU `tar' is known to work. * A working ANSI C++ compiler. `gcc' >= 2.8.1, `egcs' >= 1.0.2, SGI C++ and SunPro C++ are some of the compilers that are known to work. `libg++' is not needed when using `gcc'. `gcc' 2.7.x has a bug that makes it impossible to compile some perfectly legal C++ files, such as `sql/sql_base.cc'. If you only have `gcc' 2.7.x, you must upgrade your `gcc' to be able to compile *MySQL*. * A good `make' program. GNU `make' is always recommended and is sometimes required. If you have problems, we recommend trying GNU `make' 3.75 or newer. If you run into problems, *PLEASE ALWAYS USE `mysqlbug'* when posting questions to . Even if the problem isn't a bug, `mysqlbug' gathers system information that will help others solve your problem. By not using `mysqlbug', you lessen the likelihood of getting a solution to your problem! You will find `mysqlbug' in the `scripts' directory after you unpack the distribution. *Note Bug reports::. Quick installation overview --------------------------- The basic commands you must execute to install a *MySQL* source distribution are (from an unpacked `tar' file): shell> configure shell> make shell> make install shell> scripts/mysql_install_db shell> /usr/local/mysql/bin/safe_mysqld & If you start from a source RPM, then do the following. shell> rpm --rebuild MySQL-VERSION.src.rpm This will make a binary RPM that you can install. You can add new users using the `bin/mysql_setpermission' script if you install the `DBI' and `Msql-Mysql-modules' Perl modules. Here follows a more detailed description: To install a source distribution, follow the steps below, then proceed to *Note Post-installation::, for post-installation initialization and testing. 1. Pick the directory under which you want to unpack the distribution, and move into it. 2. Obtain a distribution file from one of the sites listed in *Note Getting *MySQL*: Getting MySQL. *MySQL* source distributions are provided as compressed `tar' archives and have names like `mysql-VERSION.tar.gz', where `VERSION' is a number like 3.22.27. 3. Unpack the distribution into the current directory: shell> gunzip < mysql-VERSION.tar.gz | tar xvf - This command creates a directory named `mysql-VERSION'. 4. Change into the top-level directory of the unpacked distribution: shell> cd mysql-VERSION 5. Configure the release and compile everything: shell> ./configure --prefix=/usr/local/mysql shell> make When you run `configure', you might want to specify some options. Run `./configure --help' for a list of options. *Note `configure' options: configure options, discusses some of the more useful options. If `configure' fails, and you are going to send mail to to ask for assistance, please include any lines from `config.log' that you think can help solve the problem. Also include the last couple of lines of output from `configure' if `configure' aborts. Post the bug report using the `mysqlbug' script. *Note Bug reports::. If the compile fails, see *Note Compilation problems::, for help with a number of common problems. 6. Install everything: shell> make install You might need to run this command as `root'. 7. Create the *MySQL* grant tables (necessary only if you haven't installed *MySQL* before): shell> scripts/mysql_install_db Note that *MySQL* versions older than 3.22.10 started the *MySQL* server when you run `mysql_install_db'. This is no longer true! 8. If you want to install support for the Perl `DBI'/`DBD' interface, see *Note Perl support::. 9. If you would like *MySQL* to start automatically when you boot your machine, you can copy `support-files/mysql.server' to the location where your system has its startup files. More information can be found in the `support-files/mysql.server' script itself, and in *Note Automatic start::. After everything has been installed, you should initialize and test your distribution. You can start the *MySQL* server with the following command, where `BINDIR' is the directory in which `safe_mysqld' is installed (`/usr/local/bin' by default): shell> BINDIR/safe_mysqld & If that command fails immediately with `mysqld daemon ended' then you can find some information in the file `mysql-data-directory/'hostname'.err'. The likely reason is that you already have another `mysqld' server running. *Note Multiple servers::. *Note Post-installation::. Applying patches ---------------- Sometimes patches appear on the mailing list or are placed in the patches area (ftp://www.mysql.com/pub/mysql/Downloads/Patches) of the *MySQL* FTP site. To apply a patch from the mailing list, save the message in which the patch appears in a file, change into the top-level directory of your *MySQL* source tree and run these commands: shell> patch -p1 < patch-file-name shell> rm config.cache shell> make clean Patches from the FTP site are distributed as plain text files or as files compressed with `gzip' files. Apply a plain patch as shown above for mailing list patches. To apply a compressed patch, change into the top-level directory of your *MySQL* source tree and run these commands: shell> gunzip < patch-file-name.gz | patch -p1 shell> rm config.cache shell> make clean After applying a patch, follow the instructions for a normal source install, beginning with the `./configure' step. After running the `make install' step, restart your *MySQL* server. You may need to bring down any currently running server before you run `make install'. (Use `mysqladmin shutdown' to do this.) Some systems do not allow you to install a new version of a program if it replaces the version that is currently executing. Typical `configure' options --------------------------- The `configure' script gives you a great deal of control over how you configure your *MySQL* distribution. Typically you do this using options on the `configure' command line. You can also affect `configure' using certain environment variables. For a list of options supported by `configure', run this command: shell> ./configure --help Some of the more commonly-used `configure' options are described below: * To compile just the *MySQL* client libraries and client programs and not the server, use the `--without-server' option: shell> ./configure --without-server If you don't have a C++ compiler, `mysql' will not compile (it is the one client program that requires C++). In this case, you can remove the code in `configure' that tests for the C++ compiler and then run `./configure' with the `--without-server' option. The compile step will still try to build `mysql', but you can ignore any warnings about `mysql.cc'. (If `make' stops, try `make -k' to tell it to continue with the rest of the build even if errors occur.) * If you don't want your log files and database directories located under `/usr/local/var', use a `configure' command something like one of these: shell> ./configure --prefix=/usr/local/mysql shell> ./configure --prefix=/usr/local \ --localstatedir=/usr/local/mysql/data The first command changes the installation prefix so that everything is installed under `/usr/local/mysql' rather than the default of `/usr/local'. The second command preserves the default installation prefix, but overrides the default location for database directories (normally `/usr/local/var') and changes it to `/usr/local/mysql/data'. * If you are using Unix and you want the *MySQL* socket located somewhere other than the default location (normally in the directory `/tmp' or `/var/run', use a `configure' command like this: shell> ./configure --with-unix-socket-path=/usr/local/mysql/tmp/mysql.sock Note that the given file must be an absolute pathname! * If you want to compile statically-linked programs (e.g., to make a binary distribution, to get more speed or to work around problems with some RedHat distributions), run `configure' like this: shell> ./configure --with-client-ldflags=-all-static \ --with-mysqld-ldflags=-all-static * If you are using `gcc' and don't have `libg++' or `libstdc++' installed, you can tell `configure' to use `gcc' as your C++ compiler: shell> CC=gcc CXX=gcc ./configure When you use `gcc' as your C++ compiler, it will not attempt to link in `libg++' or `libstdc++'. If the build fails and produces errors about your compiler or linker not being able to create the shared library `libmysqlclient.so.#' (`#' is a version number), you can work around this problem by giving the `--disable-shared' option to `configure'. In this case, `configure' will not build a shared `libmysqlclient.so.#' library. * You can configure *MySQL* not to use `DEFAULT' column values for non-`NULL' columns (i.e., columns that are not allowed to be `NULL'). This causes `INSERT' statements to generate an error unless you explicitly specify values for all columns that require a non-`NULL' value. To suppress use of default values, run `configure' like this: shell> CXXFLAGS=-DDONT_USE_DEFAULT_FIELDS ./configure * By default, *MySQL* uses the ISO-8859-1 (Latin1) character set. To change the default set, use the `--with-charset' option: shell> ./configure --with-charset=CHARSET `CHARSET' may be one of `big5', `cp1251', `cp1257', `czech', `danish',`dec8', `dos', `euc_kr', `german1', `hebrew', `hp8', `hungarian', `koi8_ru', `koi8_ukr', `latin1', `latin2', `sjis', `swe7', `tis620', `ujis', `usa7', `win1251' or `win1251ukr'. *Note Character sets::. Note that if you want to change the character set, you must do a `make distclean' between configurations! If you want to convert characters between the server and the client, you should take a look at the `SET OPTION CHARACTER SET' command. *Note `SET OPTION': SET OPTION. *Warning:* If you change character sets after having created any tables, you will have to run `isamchk -r -q' on every table. Your indexes may be sorted incorrectly otherwise. (This can happen if you install *MySQL*, create some tables, then reconfigure *MySQL* to use a different character set and reinstall it.) * To configure *MySQL* with debugging code, use the `--with-debug' option: shell> ./configure --with-debug This causes a safe memory allocator to be included that can find some errors and that provides output about what is happening. *Note Debugging server::. * Options that pertain to particular systems can be found in the system-specific sections later in this chapter. *Note Source install system issues::. Problems compiling? =================== All *MySQL* programs compile cleanly for us with no warnings on Solaris using `gcc'. On other systems, warnings may occur due to differences in system include files. See *Note MIT-pthreads::, for warnings that may occur when using MIT-pthreads. For other problems, check the list below. The solution to many problems involves reconfiguring. If you do need to reconfigure, take note of the following: * If `configure' is run after it already has been run, it may use information that was gathered during its previous invocation. This information is stored in `config.cache'. When `configure' starts up, it looks for that file and reads its contents if it exists, on the assumption that the information is still correct. That assumption is invalid when you reconfigure. * Each time you run `configure', you must run `make' again to recompile. However, you may want to remove old object files from previous builds first, since they were compiled using different configuration options. To prevent old configuration information or object files from being used, run these commands before rerunning `configure': shell> rm config.cache shell> make clean Alternatively, you can run `make distclean'. The list below describes some of the problems compiling *MySQL* that have been found to occur most often: * If you get errors when compiling `sql_yacc.cc' such as the ones shown below, you have probably run out of memory or swap space: Internal compiler error: program cc1plus got fatal signal 11 or Out of virtual memory or Virtual memory exhausted The problem is that `gcc' requires huge amounts of memory to compile `sql_yacc.cc' with inline functions. Try running `configure' with the `--with-low-memory' option: shell> ./configure --with-low-memory This option causes `-fno-inline' to be added to the compile line if you are using `gcc' and `-O0' if you are using something else. You should try the `--with-low-memory' option even if you have so much memory and swap space that you think you can't possibly have run out. This problem has been observed to occur even on systems with generous hardware configurations, and the `--with-low-memory' option usually fixes it. * By default, `configure' picks `c++' as the compiler name and GNU `c++' links with `-lg++'. If you are using `gcc', that behavior can cause problems during configuration such as this: configure: error: installation or configuration problem: C++ compiler cannot create executables. You might also observe problems during compilation related to `g++', `libg++' or `libstdc++'. One cause of these problems is that you may not have `g++', or you may have `g++' but not `libg++' or `libstdc++'. Take a look at the `config.log' file. It should contain the exact reason why your c++ compiler didn't work! To work around these problems, you can use `gcc' as your C++ compiler. Try setting the environment variable `CXX' to `"gcc -O3"'. For example: shell> CXX="gcc -O3" ./configure This works because `gcc' compiles C++ sources as well as `g++' does, but does not link in `libg++' or `libstdc++' by default. Another way to fix these problems, of course, is to install `g++', `libg++' and `libstdc++'. * If your compile fails with errors such as any of the following, you must upgrade your version of `make' to GNU `make': making all in mit-pthreads make: Fatal error in reader: Makefile, line 18: Badly formed macro assignment or make: file `Makefile' line 18: Must be a separator (: or pthread.h: No such file or directory Solaris and FreeBSD are known to have troublesome `make' programs. GNU `make' version 3.75 is known to work. * If you want to define flags to be used by your C or C++ compilers, do so by adding the flags to the `CFLAGS' and `CXXFLAGS' environment variables. You can also specify the compiler names this way using `CC' and `CXX'. For example: shell> CC=gcc shell> CFLAGS=-O6 shell> CXX=gcc shell> CXXFLAGS=-O6 shell> export CC CFLAGS CXX CXXFLAGS See *Note TcX binaries::, for a list of flag definitions that have been found to be useful on various systems. * If you get an error message like this, you need to upgrade your `gcc' compiler: client/libmysql.c:273: parse error before `__attribute__' `gcc' 2.8.1 is known to work, but we recommend using `egcs' 1.0.3a or newer instead. * If you get errors such as those shown below when compiling `mysqld', `configure' didn't correctly detect the type of the last argument to `accept()', `getsockname()' or `getpeername()': cxx: Error: mysqld.cc, line 645: In this statement, the referenced type of the pointer value "&length" is "unsigned long", which is not compatible with "int". new_sock = accept(sock, (struct sockaddr *)&cAddr, &length); To fix this, edit the `config.h' file (which is generated by `configure'). Look for these lines: /* Define as the base type of the last arg to accept */ #define SOCKET_SIZE_TYPE XXX Change `XXX' to `size_t' or `int', depending on your operating system. (Note that you will have to do this each time you run `configure', since `configure' regenerates `config.h'.) * The `sql_yacc.cc' file is generated from `sql_yacc.yy'. Normally the build process doesn't need to create `sql_yacc.cc', because *MySQL* comes with an already-generated copy. However, if you do need to recreate it, you might encounter this error: "sql_yacc.yy", line xxx fatal: default action causes potential... This is a sign that your version of `yacc' is deficient. You probably need to install `bison' (the GNU version of `yacc') and use that instead. * If you need to debug `mysqld' or a *MySQL* client, run `configure' with the `--with-debug' option, then recompile and link your clients with the new client library. *Note Debugging client::. MIT-pthreads notes ================== This section describes some of the issues involved in using MIT-pthreads. Note that on Linux you should NOT use MIT-pthreads but install LinuxThreads! *Note Linux::. If your system does not provide native thread support, you will need to build *MySQL* using the MIT-pthreads package. This includes most FreeBSD systems, SunOS 4.x, Solaris 2.4 and earlier, and some others. *Note Which OS::. * On most systems, you can force MIT-pthreads to be used by running `configure' with the `--with-mit-threads' option: shell> ./configure --with-mit-threads Building in a non-source directory is not supported when using MIT-pthreads, because we want to minimize our changes to this code. * MIT-pthreads doesn't support the `AF_UNIX' protocol used to implement Unix sockets. This means that if you compile using MIT-pthreads, all connections must be made using TCP/IP (which is a little slower). If you find after building *MySQL* that you cannot connect to the local server, it may be that your client is attempting to connect to `localhost' using a Unix socket as the default. Try making a TCP/IP connection with `mysql' by using a host option (`-h' or `--host') to specify the local host name explicitly. * The checks that determine whether or not to use MIT-pthreads occur only during the part of the configuration process that deals with the server code. If you have configured the distribution using `--without-server' to build only the client code, clients will not know whether or not MIT-pthreads is being used and will use Unix socket connections by default. Since Unix sockets do not work under MIT-pthreads, this means you will need to use `-h' or `--host' when you run client programs. * When *MySQL* is compiled using MIT-pthreads, system locking is disabled by default for performance reasons. You can tell the server to use system locking with the `--use-locking' option. * Sometimes the pthread `bind()' command fails to bind to a socket without any error message (at least on Solaris). The result is that all connections to the server fail. For example: shell> mysqladmin version mysqladmin: connect to server at '' failed; error: 'Can't connect to mysql server on localhost (146)' The solution to this is to kill the `mysqld' server and restart it. This has only happened to us when we have forced the server down and done a restart immediately. * With MIT-pthreads, the `sleep()' system call isn't interruptible with `SIGINT' (break). This is only noticeable when you run `mysqladmin --sleep'. You must wait for the `sleep()' call to terminate before the interrupt is served and the process stops. * When linking you may receive warning messages like these (at least on Solaris); they can be ignored: ld: warning: symbol `_iob' has differing sizes: (file /my/local/pthreads/lib/libpthread.a(findfp.o) value=0x4; file /usr/lib/libc.so value=0x140); /my/local/pthreads/lib/libpthread.a(findfp.o) definition taken ld: warning: symbol `__iob' has differing sizes: (file /my/local/pthreads/lib/libpthread.a(findfp.o) value=0x4; file /usr/lib/libc.so value=0x140); /my/local/pthreads/lib/libpthread.a(findfp.o) definition taken * Some other warnings also can be ignored: implicit declaration of function `int strtoll(...)' implicit declaration of function `int strtoul(...)' * We haven't gotten `readline' to work with MIT-pthreads. (This isn't needed, but may be interesting for someone.) Perl installation comments ========================== Installing Perl on Unix ----------------------- Perl support for *MySQL* is provided by means of the `DBI'/`DBD' client interface. *Note Perl::. The Perl `DBD'/`DBI' client code requires Perl 5.004 or later. The interface *will not work* if you have an older version of Perl. *MySQL* Perl support also requires that you've installed *MySQL* client programming support. If you installed *MySQL* from RPM files, client programs are in the client RPM, but client programming support is in the developer RPM. Make sure you've installed the latter RPM. As of release 3.22.8, Perl support is distributed separately from the main *MySQL* distribution. If you want to install Perl support, the files you will need can be obtained from `http://www.mysql.com/Contrib'. The Perl distributions are provided as compressed `tar' archives and have names like `MODULE-VERSION.tar.gz', where `MODULE' is the module name and `VERSION' is the version number. You should get the `Data-Dumper', `DBI', and `Msql-Mysql-modules' distributions and install them in that order. The installation procedure is shown below. The example shown is for the `Data-Dumper' module, but the procedure is the same for all three distributions. 1. Unpack the distribution into the current directory: shell> gunzip < Data-Dumper-VERSION.tar.gz | tar xvf - This command creates a directory named `Data-Dumper-VERSION'. 2. Change into the top-level directory of the unpacked distribution: shell> cd Data-Dumper-VERSION 3. Build the distribution and compile everything: shell> perl Makefile.PL shell> make shell> make test shell> make install The `make test' command is important, because it verifies that the module is working. Note that when you run that command during the `Msql-Mysql-modules' installation to exercise the interface code, the *MySQL* server must be running or the test will fail. It is a good idea to rebuild and reinstall the `Msql-Mysql-modules' distribution whenever you install a new release of *MySQL*, particularly if you notice symptoms such as all your `DBI' scripts dumping core after you upgrade *MySQL*. If you don't have the right to install Perl modules in the system directory or if you to install local Perl modules, the following reference may help you: `http://www.iserver.com/support/contrib/perl5/modules.html' Look under the heading `Installing New Modules that Require Locally Installed Modules'. Installing ActiveState Perl on Win32 ------------------------------------ To install the *MySQL* `DBD' module with ActiveState Perl on Win32, you should do the following: * Open a DOS shell. * If required, set the HTTP_proxy variable. For example, you might try: `set HTTP_proxy=my.proxy.com:3128' * Start the PPM program: `C:\perl\bin\ppm.pl' * If you have not already done so, install `DBI': `install DBI' * If this succeeds, install `DBD::mysql:' `http://www.mysql.com/Contrib/ppd/DBD-mysql.ppd' If you can't get the above to work, you should instead install the *MyODBC* driver and connect to *MySQL* server through ODBC. use DBI; $dbh= DBI->connect("DBI:ODBC:$dsn","$user","$password") || die "Got error $DBI::errstr when connecting to $dsn\n"; Installing the MySQL Perl distribution on Win32 ----------------------------------------------- The *MySQL* Perl distribution contains `DBI', `DBD:MySQL' and `DBD:ODBC'. * Get the Perl distribution for Win32 from `http://www.mysql.com/download.html'. * Unzip the distribution in `C:' so that you get a `C:\PERL' directory. * Add the directory `C:\PERL\BIN' to your path. * Add the directory `C:\PERL\BIN\MSWin32-x86-thread' or `C:\PERL\BIN\MSWin32-x86' to your path. * Test that `perl' works by executing `perl -v' in a DOS shell. Problems using the Perl `DBI'/`DBD' interface --------------------------------------------- If Perl reports that it can't find the `../mysql/mysql.so' module, then the problem is probably that Perl can't locate the shared library `libmysqlclient.so'. You can fix this by any of the following methods: * Compile the `Msql-Mysql-modules' distribution with `perl Makefile.PL -static' rather than `perl Makefile.PL' * Copy `libmysqlclient.so' to the directory where your other shared libraries are located (probably `/usr/lib' or `/lib'). * On `Linux' you can add the pathname of the directory where `libmysqlclient.so' is located to the `/etc/ld.so.conf' file. * Add the pathname of the directory where `libmysqlclient.so' is located to the `LD_RUN_PATH' environment variable. If you get the following errors from `DBD-mysql', you are probably using `gcc' (or using an old binary compiled with `gcc'): /usr/bin/perl: can't resolve symbol '__moddi3' /usr/bin/perl: can't resolve symbol '__divdi3' Add `-L/usr/lib/gcc-lib/... -lgcc' to the link command when the `mysql.so' library gets built (check the output from `make' for `mysql.so' when you compile the Perl client). The `-L' option should specify the pathname of the directory where `libgcc.a' is located on your system. Another cause of this problem may be that Perl and *MySQL* aren't both compiled with `gcc'. In this case, you can solve the mismatch by compiling both with `gcc'. If you want to use the Perl module on a system that doesn't support dynamic linking (like SCO) you can generate a static version of Perl that includes `DBI' and `DBD-mysql'. The way this works is that you generate a version of Perl with the `DBI' code linked in and install it on top of your current Perl. Then you use that to build a version of Perl that additionally has the `DBD' code linked in, and install that. On SCO, you must have the following environment variables set: shell> LD_LIBRARY_PATH=/lib:/usr/lib:/usr/local/lib:/usr/progressive/lib or shell> LD_LIBRARY_PATH=/usr/lib:/lib:/usr/local/lib:/usr/ccs/lib:/usr/progressive/lib:/usr/skunk/lib shell> LIBPATH=/usr/lib:/lib:/usr/local/lib:/usr/ccs/lib:/usr/progressive/lib:/usr/skunk/lib shell> MANPATH=scohelp:/usr/man:/usr/local1/man:/usr/local/man:/usr/skunk/man: First, create a Perl that includes a statically-linked `DBI' by running these commands in the directory where your `DBI' distribution is located: shell> perl Makefile.PL LINKTYPE=static shell> make shell> make install shell> make perl Then you must install the new Perl. The output of `make perl' will indicate the exact `make' command you will need to execute to perform the installation. On SCO, this is `make -f Makefile.aperl inst_perl MAP_TARGET=perl'. Next, use the just-created Perl to create another Perl that also includes a statically-linked `DBD::mysql' by running these commands in the directory where your `Msql-Mysql-modules' distribution is located: shell> perl Makefile.PL LINKTYPE=static shell> make shell> make install shell> make perl Finally, you should install this new Perl. Again, the output of `make perl' indicates the command to use. System-specific issues ====================== The following sections indicate some of the issues that have been observed to occur on particular systems when installing *MySQL* from a source distribution. Solaris notes ------------- On Solaris, you may run into trouble even before you get the *MySQL* distribution unpacked! Solaris `tar' can't handle long file names, so you may see an error like this when you unpack *MySQL*: x mysql-3.22.12-beta/bench/Results/ATIS-mysql_odbc-NT_4.0-cmp-db2,informix,ms-sql,mysql,oracle,solid,sybase, 0 bytes, 0 tape blocks tar: directory checksum error In this case, you must use GNU `tar' (`gtar') to unpack the distribution. You can find a precompiled copy for Solaris at `http://www.mysql.com/Downloads/'. Sun native threads work only on Solaris 2.5 and higher. For 2.4 and earlier versions, *MySQL* will automatically use MIT-pthreads. *Note MIT-pthreads::. If you get the following error from configure: checking for restartable system calls... configure: error can not run test programs while cross compiling This means that you have something wrong with your compiler installation! In this case you should upgrade your compiler to a newer version. You may also be able to solve this problem by inserting the following row into the `config.cache' file: ac_cv_sys_restartable_syscalls=${ac_cv_sys_restartable_syscalls='no'} If you are using Solaris on a SPARC, the recommended compiler is `egcs' 1.1.2 or newer. You can find this at `http://egcs.cygnus.com/'. Note that `egs' 1.1.1 and `gcc' 2.8.1 don't work reliably on SPARC! The recommended `configure' line when using `egcs' 1.1.2 is: shell> CC=gcc CFLAGS="-O6" \ CXX=gcc CXXFLAGS="-O6 -felide-constructors -fno-exceptions -fno-rtti" \ ./configure --prefix=/usr/local/mysql --with-low-memory If you have the Sun Workshop 4.2 compiler, you can run `configure' like this: CC=cc CFLAGS="-xstrconst -Xa -xO4 -native -mt" CXX=CC CXXFLAGS="-xO4 -native -noex -mt" ./configure -prefix=/usr/local/mysql shell> CC=cc CFLAGS="-Xa -fast -xO4 -native -xstrconst -mt" \ CXX=CC CXXFLAGS="-noex -XO4 -mt" \ ./configure You may also have to edit the `configure' script to change this line: #if !defined(__STDC__) || __STDC__ != 1 to this: #if !defined(__STDC__) If you turn on `__STDC__' with the `-Xc' option, the Sun compiler can't compile with the Solaris `pthread.h' header file. This is a Sun bug (broken compiler or broken include file). If `mysqld' issues the error message shown below when you run it, you have tried to compile *MySQL* with the Sun compiler without enabling the multi-thread option (`-mt'): libc internal error: _rmutex_unlock: rmutex not held Add `-mt' to `CFLAGS' and `CXXFLAGS' and try again. If you get the following error when compiling *MySQL* with `gcc', it means that your `gcc' is not configured for your version of Solaris! shell> gcc -O3 -g -O2 -DDBUG_OFF -o thr_alarm ... ./thr_alarm.c: In function `signal_hand': ./thr_alarm.c:556: too many arguments to function `sigwait' The proper thing to do in this case is to get the newest version of `egcs' and compile it with your current `gcc' compiler! At least for Solaris 2.5, almost all binary versions of `gcc' have old, unusable include files that will break all programs that use threads (and possibly other programs)! Solaris doesn't provide static versions of all system libraries (`libpthreads' and `libdl'), so you can't compile *MySQL* with `--static'. If you try to do so, you will get the error: ld: fatal: library -ldl: not found If too many processes try to connect very rapidly to `mysqld', you will see this error in the *MySQL* log: Error in accept: Protocol error You might try starting the server with the `--set-variable back_log=50' option as a workaround for this. If you are linking your own *MySQL* client, you might get the following error when you try to execute it: ld.so.1: ./my: fatal: libmysqlclient.so.#: open failed: No such file or directory The problem can be avoided by one of the following methods: * Link the client with the following flag (instead of `-Lpath'): `-Wl,r/full-path-to-libmysqlclient.so'. * Copy `libmysqclient.so' to `/usr/lib'. * Add the pathname of the directory where `libmysqlclient.so' is located to the `LD_RUN_PATH' environment variable before running your client. Solaris 2.7 notes ----------------- You can normally use a Solaris 2.6 binary on Solaris 2.7. Most of the Solaris 2.6 issues also apply for Solaris 2.7. Note that *MySQL* 3.23.4 and above should be able to autodetect Solaris 2.7 and enable workarounds for the following problems! Solaris 2.7 has some bugs in the include files. You may see the following error when you use `gcc': /usr/include/widec.h:42: warning: `getwc' redefined /usr/include/wchar.h:326: warning: this is the location of the previous definition If this occurs, you can do the following to fix the problem: Copy `/usr/include/widec.h' to `.../lib/gcc-lib/os/gcc-version/include' and change line 41 from: #if !defined(lint) && !defined(__lint) to #if !defined(lint) && !defined(__lint) && !defined(getwc) Alternatively, you can edit `/usr/include/widec.h' directly. Either way, after you make the fix, you should remove `config.cache' and run `configure' again! If you get errors like this when you run `make', it's because `configure' didn't detect the `curses.h' file (probably because of the error in `/usr/include/widec.h': In file included from mysql.cc:50: /usr/include/term.h:1060: syntax error before `,' /usr/include/term.h:1081: syntax error before `;' The solution to this is to do one of the following steps: * Edit `/usr/include/widec.h' as indicted above and rerun configure * Remove the `#define HAVE_TERM' line from `config.h' file and run `make' again. * Configure with `CFLAGS=-DHAVE_CURSES CXXFLAGS=-DHAVE_CURSES ./configure' Solaris x86 notes ----------------- If you are using `gcc' or `egcs' on Solaris x86 and you experience problems with core dumps under load, you should use the following `configure' command: shell> CC=gcc CFLAGS="-O6 -fomit-frame-pointer" \ CXX=gcc \ CXXFLAGS="-O6 -fomit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" \ ./configure --prefix=/usr/local/mysql This will avoid problems with the `libstdc++' library and with C++ exceptions. If this doesn't help, you should compile a debug version and run it with a trace file or under `gdb'. *Note Debugging server::. SunOS 4 notes ------------- On SunOS 4, MIT-pthreads is needed to compile *MySQL*, which in turn means you will need GNU `make'. Some SunOS 4 systems have problems with dynamic libraries and `libtool'. You can use the following `configure' line to avoid this problem: shell> ./configure --disable-shared --with-mysqld-ldflags=-all-static When compiling `readline', you may get warnings about duplicate defines. These may be ignored. When compiling `mysqld', there will be some `implicit declaration of function' warnings. These may be ignored. Linux notes (all Linux versions) -------------------------------- *MySQL* uses LinuxThreads on Linux. If you are using an old Linux version that doesn't have `glibc2', you must install LinuxThreads before trying to compile *MySQL*. `http://www.mysql.com/Downloads/Linux' If you can't start `mysqld' or if `mysql_install_db' doesn't work, please continue reading! This only happens on Linux system with problems in the LinuxThreads or `libc'/`glibc' libraries. There are a lot of simple workarounds to get *MySQL* to work! The simplest is to use the binary version of *MySQL* (not the RPM) for Linux x86. One nice aspect of this version is that it's probably 10% faster than any version you would compile yourself! *Note Compile and link options::. One known problem with the binary distribution is that with older Linux systems that use `libc' (like RedHat 4.x or Slackware), you will get some non-fatal problems with hostname resolution *Note Binary notes-Linux::. `isamchk' hangs with `libc.so.5.3.12'. Upgrading to the newest `libc' fixes this problem. When using LinuxThreads you will see a minimum of three processes running. These are in fact threads. There will be one thread for the LinuxThreads manager, one thread to handle connections, and one thread to handle alarms and signals. If you see a dead `mysqld' daemon process with `ps', this usually means that you have found a bug in *MySQL* or you have got a corrupted table. *Note Crashing::. If you are using LinuxThreads and `mysqladmin shutdown' doesn't work, you must upgrade to LinuxThreads 0.7.1 or newer. If you are using RedHat, you might get errors like this: /usr/bin/perl is needed... /usr/sh is needed... /usr/sh is needed... If so, you should upgrade your version of `rpm' to `rpm-2.4.11-1.i386.rpm' and `rpm-devel-2.4.11-1.i386.rpm' (or later). You can get the upgrades of libraries to RedHat 4.2 from `ftp://ftp.redhat.com/updates/4.2/i386'. Or `http://www.sunsite.unc.edu/pub/Linux/distributions/redhat/code/rpm/' for other distributions. If you are linking your own *MySQL* client and get the error: ld.so.1: ./my: fatal: libmysqlclient.so.4: open failed: No such file or directory when executing them, the problem can be avoided by one of the following methods: * Link the client with the following flag (instead of `-Lpath'): `-Wl,r/path-libmysqlclient.so'. * Copy `libmysqclient.so' to `/usr/lib'. * Add the pathname of the directory where `libmysqlclient.so' is located to the `LD_RUN_PATH' environment variable before running your client. If you are using the Fujitsu compiler `(fcc / FCC)' you will have some problems compiling *MySQL* because the Linux header files are very `gcc' oriented. The following `configure' line should work with `fcc/FCC': CC=fcc CFLAGS="-O -K fast -K lib -K omitfp -Kpreex -D_GNU_SOURCE -DCONST=const -DNO_STRTOLL_PROTO" CXX=FCC CXXFLAGS="-O -K fast -K lib -K omitfp -K preex --no_exceptions --no_rtti -D_GNU_SOURCE -DCONST=const -Dalloca=__builtin_alloca -DNO_STRTOLL_PROTO '-D_EXTERN_INLINE=static __inline'" ./configure --prefix=/usr/local/mysql --enable-assembler --with-mysqld-ldflags=-all-static --disable-shared --with-low-memory Linux-x86 notes ............... *MySQL* requires `libc' version 5.4.12 or newer. It's known to work with `libc' 5.4.46. `glibc' version 2.0.6 and later should also work. There have been some problems with the `glibc' RPMs from RedHat so if you have problems, check whether or not there are any updates! The `glibc' 2.0.7-19 and 2.0.7-29 RPMs are known to work. On some older Linux distributions, `configure' may produce an error like this: Syntax error in sched.h. Change _P to __P in the /usr/include/sched.h file. See the Installation chapter in the Reference Manual. Just do what the error message says and add an extra underscore to the `_P' macro that has only one underscore, then try again. You may get some warnings when compiling; those shown below can be ignored: mysqld.cc -o objs-thread/mysqld.o mysqld.cc: In function `void init_signals()': mysqld.cc:315: warning: assignment of negative value `-1' to `long unsigned int' mysqld.cc: In function `void * signal_hand(void *)': mysqld.cc:346: warning: assignment of negative value `-1' to `long unsigned int' In Debian GNU/Linux, if you want *MySQL* to start automatically when the system boots, do the following: shell> cp support-files/mysql.server /etc/init.d/mysql.server shell> /usr/sbin/update-rc.d mysql.server defaults 99 `mysql.server' can be found in the `share/mysql' directory under the *MySQL* installation directory, or in the `support-files' directory of the *MySQL* source tree. If `mysqld' always core dumps when it starts up, the problem may be that you have an old `/lib/libc.a'. Try renaming it, then remove `sql/mysqld' and do a new `make install' and try again. This problem has been reported on some Slackware installations. RedHat 5.0 has also a similar problem with some new `glibc' versions. *Note Linux-RedHat50::. If you get the following error when linking `mysqld', it means that your `libg++.a' is not installed correctly: /usr/lib/libc.a(putc.o): In function `_IO_putc': putc.o(.text+0x0): multiple definition of `_IO_putc' You can avoid using `libg++.a' by running `configure' like this: shell> CXX=gcc ./configure RedHat 5.0 notes ................ If you have any problems with *MySQL* on RedHat, you should start by upgrading `glibc' to the newest possible version! If you install all the official RedHat patches (including `glibc-2.0.7-19' and `glibc-devel-2.0.7-19'), both the binary and source distributions of *MySQL* should work without any trouble! The updates are needed since there is a bug in `glibc' 2.0.5 in how `pthread_key_create' variables are freed. With `glibc' 2.0.5, you must use a statically-linked *MySQL* binary distribution. If you want to compile from source, you must install the corrected version of LinuxThreads from `http://www.mysql.com/Downloads/Linux' or upgrade your `glibc'. If you have an incorrect version of `glibc' or LinuxThreads, the symptom is that `mysqld' crashes after each connection. For example, `mysqladmin version' will crash `mysqld' when it finishes! Another symptom of incorrect libraries is that `mysqld' crashes at once when it starts. On some Linux systems, this can be fixed by configuring like this: shell> ./configure --with-mysqld-ldflags=-all-static On Redhat 5.0, the easy way out is to install the `glibc' 2.0.7-19 RPM and run `configure' *without* the `--with-mysqld-ldflags=-all-static' option. For the source distribution of `glibc' 2.0.7, a patch that is easy to apply and is tested with *MySQL* may be found at: `http://www.mysql.com/Download/Linux/glibc-2.0.7-total-patch.tar.gz' If you experience crashes like these when you build *MySQL*, you can always download the newest binary version of *MySQL*. This is statically-linked to avoid library conflicts and should work on all Linux systems! *MySQL* comes with an internal debugger that can generate trace files with a lot of information that can be used to find and solve a wide range of different problems. *Note Debugging server::. RedHat 5.1 notes ................ The `glibc' of RedHat 5.1 (`glibc' 2.0.7-13) has a memory leak, so to get a stable *MySQL* version, you must upgrade `glibc' to 2.0.7-19, downgrade `glibc' or use a binary version of `mysqld'. If you don't do this, you will encounter memory problems (out of memory, etc., etc.). The most common error in this case is: Can't create a new thread (errno 11). If you are not out of available memory, you can consult the manual for any possible OS dependent bug After you have upgraded to `glibc' 2.0.7-19, you can configure *MySQL* with dynamic linking (the default), but you *cannot* run `configure' with the `--with-mysqld-ldflags=-all-static' option until you have installed `glibc' 2.0.7-19 from source! You can check which version of `glibc' you have with `rpm -q glibc'. Linux-SPARC notes ................. In some implementations, `readdir_r()' is broken. The symptom is that `SHOW DATABASES' always returns an empty set. This can be fixed by removing `HAVE_READDIR_R' from `config.h' after configuring and before compiling. Some problems will require patching your Linux installation. The patch can be found at `http://www.mysql.com/patches/Linux-sparc-2.0.30.diff'. This patch is against the Linux distribution `sparclinux-2.0.30.tar.gz' that is available at `vger.rutgers.edu' (a version of Linux that was never merged with the official 2.0.30). You must also install LinuxThreads 0.6 or newer. Thanks to for this information. Linux-Alpha notes ................. The big problem on Linux-Alpha is that there are still some problems with threads in `glibc' on this platform. You should start by getting the newest `glibc' version you can find. Note that before you run any programs that use threads (like `mysqld', `thr_alarm' or `thr_lock'), you should raise the shared memory limit (with `ulimit'). The *MySQL* benchmarks are known to fail if you forget to do this! Configure *MySQL* with the following command: shell> CC=gcc CCFLAGS="-Dalpha_linux_port" \ CXX=gcc CXXFLAGS="-O3 -Dalpha_linux_port -felide-constructors -fno-exceptions -fno-rtti" \ ./configure --prefix=/usr/local/mysql Try to compile `mysys/thr_lock' and `mysys/thr_alarm'. Test that these programs work! (Invoke each one with no arguments. Each should end with `test_succeeded' if everything was okay.) After installing *MySQL*, uncomment the `ulimit' command in `safe_mysqld' and add options to increase shared memory. Note that Linux-Alpha is still an alpha-quality platform for *MySQL*. With the newest `glibc', you have a very good chance of it working. If you have problems with signals (*MySQL* dies unexpectedly under high load) you may have found an OS bug with threads and signals. In this case you can tell *MySQL* not to use signals by configuring with: shell> CFLAGS=-DDONT_USE_THR_ALARM \ CXXFLAGS=-DDONT_USE_THR_ALARM \ ./configure ... This doesn't affect the performance of *MySQL*, but has the side effect that you can't kill clients that are "sleeping" on a connection with `mysqladmin kill' or `mysqladmin shutdown'. Instead, the client will die when it issues its next command. MkLinux notes ............. *MySQL* should work on MkLinux with the newest `glibc' package (tested with `glibc' 2.0.7). Qube2 Linux notes ................. To get *MySQL* to work on Qube2, (Linux Mips), you need the newest `glibc' libraries (`glibc-2.0.7-29C2' is known to work). You must also use the `egcs' C++ compiler (`egcs-1.0.2-9' or newer). Alpha-DEC-Unix notes -------------------- When compiling threaded programs under Digital UNIX, the documentation recommends using the `-pthread' option for `cc' and `cxx' and the libraries `-lmach -lexc' (in addition to `-lpthread'). You should run `configure' something like this: shell> CC="cc -pthread" CXX="cxx -pthread -O" \ ./configure --with-named-thread-libs="-lpthread -lmach -lexc -lc" When compiling `mysqld', you may see a couple of warnings like this: mysqld.cc: In function void handle_connections()': mysqld.cc:626: passing long unsigned int *' as argument 3 of accept(int,sockadddr *, int *)' You can safely ignore these warnings. They occur because `configure' can detect only errors, not warnings. If you start the server directly from the command line, you may have problems with it dying when you log out. (When you log out, your outstanding processes receive a `SIGHUP' signal.) If so, try starting the server like this: shell> nohup mysqld [options] & `nohup' causes the command following it to ignore any `SIGHUP' signal sent from the terminal. Alternatively, start the server by running `safe_mysqld', which invokes `mysqld' using `nohup' for you. Alpha-DEC-OSF1 notes -------------------- If you have problems compiling and have DEC `CC' and `gcc' installed, try running `configure' like this: shell> CC=cc CFLAGS=-O CXX=gcc CXXFLAGS=-O3 \ ./configure --prefix=/usr/local/mysql If you get problems with the `c_asm.h' file, you can create and use a 'dummy' `c_asm.h' file with: shell> touch include/c_asm.h shell> CC=gcc CFLAGS=-I./include \ CXX=gcc CXXFLAGS=-O3 \ ./configure --prefix=/usr/local/mysql On OSF1 V4.0D and compiler "DEC C V5.6-071 on Digital UNIX V4.0 (Rev. 878)" the compiler had some strange behavior (undefined `asm' symbols). `/bin/ld' also appears to be broken (problems with `_exit undefined' errors occuring while linking `mysqld'). On this system, we have managed to compile *MySQL* with the following `configure' line, after replacing `/bin/ld' with the version from OSF 4.0C: shell> CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql In some versions of OSF1, the `alloca()' function is broken. Fix this by removing the line in `config.h' that defines `'HAVE_ALLOCA''. The `alloca()' function also may have an incorrect prototype in `/usr/include/alloca.h'. This warning resulting from this can be ignored. `configure' will use the following thread libraries automatically: `--with-named-thread-libs="-lpthread -lmach -lexc -lc"'. When using `gcc', you can also try running `configure' like this: shell> CFLAGS=-D_PTHREAD_USE_D4 CXX=gcc CXXFLAGS=-O3 ./configure .... If you have problems with signals (*MySQL* dies unexpectedly under high load) you may have found an OS bug with threads and signals. In this case you can tell *MySQL* not to use signals by configuring with: shell> CFLAGS=-DDONT_USE_THR_ALARM \ CXXFLAGS=-DDONT_USE_THR_ALARM \ ./configure ... This doesn't affect the performance of *MySQL*, but has the side effect that you can't kill clients that are "sleeping" on a connection with `mysqladmin kill' or `mysqladmin shutdown'. Instead, the client will die when it issues its next command. SGI-Irix notes -------------- You may have to undefine some things in `config.h' after running `configure' and before compiling. In some Irix implementations, the `alloca()' function is broken. If the `mysqld' server dies on some `SELECT' statements, remove the lines from `config.h' that define `HAVE_ALLOC' and `HAVE_ALLOCA_H'. If `mysqladmin create' doesn't work, remove the line from `config.h' that defines `HAVE_READDIR_R'. You may have to remove the `HAVE_TERM_H' line as well. SGI recommends that you install all of the patches on this page as a set: http://support.sgi.com/surfzone/patches/patchset/6.2_indigo.rps.html At the very minimum, you should install the latest kernel rollup, the latest `rld' rollup, and the latest `libc' rollup. You definately need all the POSIX patches on this page, for pthreads support: http://support.sgi.com/surfzone/patches/patchset/6.2_posix.rps.html If you get the something like the following error when compiling `mysql.cc': "/usr/include/curses.h", line 82: error(1084): invalid combination of type Then type the following in the top-level directory of your *MySQL* source tree: shell> extra/replace bool curses_bool < /usr/include/curses.h > include/curses.h shell> make There have also been reports of scheduling problems. If only one thread is running, things go slow. Avoid this by starting another client. This may lead to a 2-to-10-fold increase in execution speed thereafter for the other thread. This is a poorly-understood problem with Irix threads; you may have to improvise to find solutions until this can be fixed. If you are compiling with `gcc', you can use the following `configure' command: shell> CC=gcc CXX=gcc CXXFLAGS=-O3 \ ./configure --prefix=/usr/local/mysql --with-thread-safe-client --with-named-thread-libs=-lpthread FreeBSD notes ------------- The easiest and therefor the preferred way to install is to use the mysql-server and mysql-client ports available on `http://www.freebsd.org' Using these gives you: * A working *MySQL* with all optimizations known to work on your version of FreeBSD enabled. * Automatic configuration and build. * Startup scripts installed in /usr/local/etc/rc.d * Ability to see which files that are installed with pkg_info -L. And to remove them all with pkg_delete if you no longer want *MySQL* on that machine. It is recomended to use MIT-pthreads on FreeBSD 2.x and native threads on versions 3 and up. It is possible to run with with native threads on some late 2.2.x versions but you may encounter problems shutting down mysqld. Be sure to have your name resolver setup correct. Otherwise you may experience resolver delays or failures when connecting to mysqld. Make sure that the `localhost' entry in the `/etc/hosts' file is correct (otherwise you will have problems connecting to the database). The `/etc/hosts' file should start with a line: 127.0.0.1 localhost localhost.your.domain If you notice that `configure' will use MIT-pthreads, you should read the MIT-pthreads notes. *Note MIT-pthreads::. If you get an error from `make install' that it can't find `/usr/include/pthreads', `configure' didn't detect that you need MIT-pthreads. This is fixed by executing these commands: shell> rm config.cache shell> ./configure --with-mit-threads The behavior of FreeBSD `make' is slightly different from that of GNU `make'. If you have `make'-related problems, you should install GNU `make'. FreeBSD is also known to have a very low default file handle limit. *Note Not enough file handles::. Uncomment the ulimit -n section in safe_mysqld or raise the limits for the mysqld user in /etc/login.conf (and rebuild it witg cap_mkdb /etc/login.conf) also be sure you set the appropriate Class for this user in the password file if you are not using the default (use: chpass mysqld-user-name) If you have a problem with `SELECT NOW()' returning values in GMT and not your local time, you have to set the `TZ' environment variable to your current timezone. This should be done for the environment in which the server runs, for example, in `safe_mysqld' or `mysql.server'. To get a secure and stable system you should only use FreeBSD kernels that are marked `-STABLE' NetBSD notes ------------ To compile on NetBSD you need GNU `make'. Otherwise the compile will crash when `make' tries to run `lint' on C++ files. BSD/OS notes ------------ BSD/OS 2.x notes ................ If you get the following error when compiling *MySQL*, your `ulimit' value for virtual memory is too low: item_func.h: In method `Item_func_ge::Item_func_ge(const Item_func_ge &)': item_func.h:28: virtual memory exhausted make[2]: *** [item_func.o] Error 1 Try using `ulimit -v 80000' and run `make' again. If this doesn't work and you are using `bash', try switching to `csh' or `sh'; some BSDI users have reported problems with `bash' and `ulimit'. If you are using `gcc', you may also use have to use the `--with-low-memory' flag for `configure' to be able to compile `sql_yacc.cc'. If you have a problem with `SELECT NOW()' returning values in GMT and not your local time, you have to set the `TZ' environment variable to your current timezone. This should be done for the environment in which the server runs, for example in `safe_mysqld' or `mysql.server'. BSD/OS 3.x notes ................ Upgrade to BSD/OS 3.1. If that is not possible, install BSDIpatch M300-038. Use the following command when configuring *MySQL*: shell> env CXX=shlicc++ CC=shlicc2 \ ./configure \ --prefix=/usr/local/mysql \ --localstatedir=/var/mysql \ --without-perl \ --with-unix-socket-path=/var/mysql/mysql.sock The following is also known to work: shell> env CC=gcc CXX=gcc CXXFLAGS=-O3 \ ./configure \ --prefix=/usr/local/mysql \ --with-unix-socket-path=/var/mysql/mysql.sock You can change the directory locations if you wish, or just use the defaults by not specifying any locations. If you have problems with performance under heavy load, try using the `--skip-thread-priority' option to `safe_mysqld'! This will run all threads with the same priority; on BSDI 3.1, this gives better performance (at least until BSDI fixes their thread scheduler). If you get the error `virtual memory exhausted' while compiling, you should try using `ulimit -v 80000' and run `make' again. If this doesn't work and you are using `bash', try switching to `csh' or `sh'; some BSDI users have reported problems with `bash' and `ulimit'. BSD/OS 4.x notes ................ BSDI 4.x has some thread related bugs. If you want to use *MySQL* on this, you should install all thread related patches. At least M400-023 should be installed. SCO notes --------- The current port is tested only on a "sco3.2v5.0.4" and "sco3.2v5.0.5" system. There has also been a lot of progress on a port to "sco 3.2v4.2". 1. For OpenServer 5.0.X you need to use GDS in Skunkware 95 (95q4c). This is necessary because GNU `gcc' 2.7.2 in Skunkware 97 does not have GNU `as'. You can also use `egcs' 1.1.2 or newer `http://www.egcs.com/'. If you are using `egcs' 1.1.2 you have to execute the following command: shell> cp -p /usr/include/pthread/stdtypes.h /usr/local/lib/gcc-lib/i386-pc-sco3.2v5.0.5/egcs-2.91.66/include/pthread/ 2. You need the port of GCC 2.5.? for this product and the Development system. They are required on this version of SCO UNIX. You cannot just use the GCC Dev system. 3. You should get the FSU Pthreads package and install it first. This can be found at `http://www.cs.wustl.edu/~schmidt/ACE_wrappers/FSU-threads.tar.gz'. You can also get a precompiled package from `ftp://www.mysql.com/pub/mysql/Downloads/SCO/FSU-threads-3.5c.tar.gz'. 4. FSU Pthreads can be compiled with SCO UNIX 4.2 with tcpip. Or OpenServer 3.0 or Open Desktop 3.0 (OS 3.0 ODT 3.0), with the SCO Development System installed using a good port of GCC 2.5.X ODT or OS 3.0 you will need a good port of GCC 2.5.? There are a lot of problems without a good port. The port for this product requires the SCO UNIX Development system. Without it, you are missing the libraries and the linker that is needed. 5. To build FSU Pthreads on your system, do the following: 1. Run `./configure' in the `threads/src' directory and select the SCO OpenServer option. This command copies `Makefile.SCO5' to `Makefile'. 2. Run `make'. 3. To install in the default `/usr/include' directory, login as root, then `cd' to the `thread/src' directory, and run `make install'. 6. Remember to use GNU `make' when making *MySQL*. 7. On OSR 5.0.5, you should use the following configure line: shell> CC="gcc -DSCO" CXX="gcc -DSCO" ./configure The `-DSCO' is needed to help configure detect some thread functions properly. If you forget `-DSCO', you will get the following error message while compiling: my_pthread.c: In function `my_pthread_mutex_init': my_pthread.c:374: `pthread_mutexattr_default' undeclared (first use this function) 8. If you don't start `safe_mysqld' as root, you probably will get only the default 110 open files per process. `mysqld' will write a note about this in the log file. 9. With SCO 3.2V5.0.5, you should use a FSU Pthreads version 3.5c or newer. The following `configure' command should work: shell> CC="gcc -belf" ./configure --prefix=/usr/local/mysql --disable-shared 10. With SCO 3.2V4.2, you should use a FSU Pthreads version 3.5c or newer. The following `configure' command should work: shell> CFLAGS="-D_XOPEN_XPG4" CXX=gcc CXXFLAGS="-D_XOPEN_XPG4" \ ./configure \ --with-debug --prefix=/usr/local/mysql \ --with-named-thread-libs="-lgthreads -lsocket -lgen -lgthreads" \ --with-named-curses-libs="-lcurses" You may get some problems with some include files. In this case, you can find new SCO-specific include files at `ftp://www.mysql.com/pub/mysql/Downloads/SCO/SCO-3.2v4.2-includes.tar.gz'. You should unpack this file in the `include' directory of your *MySQL* source tree. SCO development notes: * *MySQL* should automatically detect FSU Pthreads and link `mysqld' with `-lgthreads -lsocket -lgthreads'. * The SCO development libraries are reentrant in FSU Pthreads. SCO claims that its libraries' functions are reentrant, so they must be reentrant with FSU Pthreads. FSU Pthreads on OpenServer tries to use the SCO scheme to make reentrant library. * FSU Pthreads (at least the version at `www.mysql.com') comes linked with GNU `malloc'. If you encounter problems with memory usage, make sure that `gmalloc.o' is included in `libgthreads.a' and `libgthreads.so'. * In FSU Pthreads, the following system calls are pthreads-aware: `read()', `write()', `getmsg()', `connect()', `accept()', `select()' and `wait()'. If you want to install DBI on SCO, you have to edit the `Makefiles' in DBI-xxx and each subdirectory: OLD: NEW: CC = cc CC = gcc -belf CCCDLFLAGS = -KPIC -W1,-Bexport CCCDLFLAGS = -fpic CCDLFLAGS = -wl,-Bexport CCDLFLAGS = LD = ld LD = gcc -belf -G -fpic LDDLFLAGS = -G -L/usr/local/lib LDDLFLAGS = -L/usr/local/lib LDFLAGS = -belf -L/usr/local/lib LDFLAGS = -L/usr/local/lib LD = ld LD = gcc -belf -G -fpic OPTIMISE = -Od OPTIMISE = -O1 OLD: CCCFLAGS = -belf -dy -w0 -U M_XENIX -DPERL_SCO5 -I/usr/local/include NEW: CCFLAGS = -U M_XENIX -DPERL_SCO5 -I/usr/local/include This is because the Perl dynaloader will not load the `DBI' modules if they were compiled with `icc' or `cc'. Perl works best when compiled with `cc'. SCO Unixware 7.0 notes ---------------------- You must use a version of *MySQL* at least as recent as 3.22.13, since that version fixes some portability problems under Unixware. We have been able to compile *MySQL* with the following `configure' command on UnixWare 7.0.1: shell> CC=cc CXX=CC ./configure --prefix=/usr/local/mysql IBM-AIX notes ------------- Automatic detection of `xlC' is missing from Autoconf, so a `configure' command something like this is needed when using the IBM compiler: shell> CC="xlc_r -ma -O3 -qstrict -DHAVE_INT_8_16_32" \ CXX="xlC_r -ma -O3 -qstrict -DHAVE_INT_8_16_32" \ ./configure If you are using `egcs' to compile *MySQL*, you *MUST* use the `-fno-exceptions' flag, as the exception handling in `egcs' is not thread-safe! (This is tested with `egcs' 1.1.) We recommend the following `configure' line with `egcs' and `gcc' on AIX: shell> CXX=gcc \ CXXFLAGS="-felide-constructors -fno-exceptions -fno-rtti" \ ./configure --prefix=/home/monty --with-debug --with-low-memory If you have problems with signals (*MySQL* dies unexpectedly under high load) you may have found an OS bug with threads and signals. In this case you can tell *MySQL* not to use signals by configuring with: shell> CFLAGS=-DDONT_USE_THR_ALARM CXX=gcc \ CXXFLAGS="-felide-constructors -fno-exceptions -fno-rtti -DDONT_USE_THR_ALARM" \ ./configure --prefix=/home/monty --with-debug --with-low-memory This doesn't affect the performance of *MySQL*, but has the side effect that you can't kill clients that are "sleeping" on a connection with `mysqladmin kill' or `mysqladmin shutdown'. Instead, the client will die when it issues its next command. HP-UX notes ----------- There are a couple of "small" problems when compiling *MySQL* on HP-UX. We recommend that you use `gcc' instead of the HP-UX native compiler, because `gcc' produces better code! We recommend one to use gcc 2.95 on HP-UX. Don't use high optimization flags (like -O6) as this may not be safe on HP-UX. Note that MIT-pthreads can't be compiled with the HP-UX compiler, because it can't compile `.S' (assembler) files. The following configure line should work: CFLAGS="-DHPUX -I/opt/dce/include" CXXFLAGS="-DHPUX -I/opt/dce/include -felide-constructors -fno-exceptions -fno-rtti" CXX=gcc ./configure --with-pthread --with-named-thread-libs='-ldce' --prefix=/usr/local/mysql --disable-shared If you are compiling `gcc' 2.95 yourself, you should NOT link it with the DCE libraries (`libdce.a' or `libcma.a') if you want to compile *MySQL* with MIT-pthreads. If you mix the DCE and MIT-pthreads packages you will get a `mysqld' to which you cannot connect. Remove the DCE libraries while you compile `gcc' 2.95! Win32 notes =========== This section describes installation and use of *MySQL* on Win32. This is also described in the `README' file that comes with the *MySQL* Win32 distribution. Installing MySQL on Win32 ------------------------- If you don't have a registered version of *MySQL*, you should first download the shareware version from: *MySQL* 3.21.29 (http://www.mysql.com/mysql_w32.htmy) If you plan to connect to *MySQL* from some other program, you will probably also need the *MyODBC* driver. You can find this at the *MySQL* download page (http://www.mysql.com/download.htmy). To install either distribution, unzip it in some empty directory and run the `Setup.exe' program. Installation takes place in `C:\mysql'. Starting MySQL on Win95 / Win98 ------------------------------- *MySQL* uses TCP/IP to connect a client to a server. (This will allow any machine on your network to connect to your *MySQL* server). Because of this, you must install TCP/IP on your machine before starting *MySQL*. You can find TCP/IP on your Windows CD-ROM. Note that if you are using an old Win95 release (for example OSR2), it's likely that you have an old Winsock package! *MySQL* requires Winsock 2! You can get the newest Winsock from Microsoft (http://www.microsoft.com). Win98 has as default the new Winsock 2 library, so the above doesn't apply for Win98. There are 2 different *MySQL* servers you can use: `mysqld' Compiled with full debugging and automatic memory allocation checking `mysqld-opt'Optimized for a Pentium processor. Both of the above should work on any Intel processor >= i386. To start the `mysqld' server, you should start a MS-DOS window and type: C:\mysql\bin\mysqld This will start `mysqld' in the background without a window. You can kill the *MySQL* server by executing: C:\mysql\bin\mysqladmin -u root shutdown Note that Win95/Win98 don't support creation of named pipes. On Win95/Win98, you can only use named pipes to connect to a remote *MySQL* running on an NT server. Starting MySQL on NT -------------------- The Win95/Win98 section also applies to *MySQL* on NT, with the following differences: To get *MySQL* to work with TCP/IP, you must install service pack 3 (or newer)! For NT, the server name is `mysqld-nt'. Normally you should install *MySQL* as a service on NT: C:\mysql\bin\mysqld-nt --install (You could use the `mysqld' or `mysqld-opt' servers on NT, but those cannot be started as a service or use named pipes.) You can start and stop the *MySQL* service with: NET START mysql NET STOP mysql Note that in this case you can't use any other options for `mysqld-nt'! You can also run `mysqld-nt' as a standalone program on NT if you need to start `mysqld-nt' with any options! If you start `mysqld-nt' without options on NT, `mysqld-nt' tries to starts itself as a service with the default service options. If you have stopped `mysqld-nt', you have to start it with `NET START mysql'. The service is installed with the name `MySql'. Once installed, it must be started using Services Control Manager (SCM) Utility (found in Control Panel) or by using the `NET START MySQL' command. If any options are desired, they must be specified as "Startup parameters" in the SCM utility before you start the *MySQL* service. Once running, `mysqld-nt' can be stopped using `mysqladmin' or from the SCM utility or by using the command `NET STOP MySQL'. If you use SCM to stop `mysqld-nt', there is a strange message from SCM about `mysqld shutdown normally'. When run as a service, `mysqld-nt' has no access to a console and so no messages can be seen. On NT you can get the following service error messages: Permission Denied Means that it cannot find `mysqld-nt.exe' Cannot Register Means that the path is incorrect If you have problems installing `mysqld-nt' as a service, try starting it with the full path: C:\mysql\bin\mysqld --install If this doesn't work, you can get `mysqld-nt' to start properly by fixing the path in the registry! If you don't want to start `mysqld-nt' as a service, you can start it as follows: C:\mysql\bin\mysqld-nt --standalone or C:\mysql\bin\mysqld-nt --standalone --debug The last version gives you a debug trace in `C:\mysqld.trace'. Running MySQL on Win32 ---------------------- *MySQL* supports TCP/IP on all Win32 platforms and named pipes on NT. The default is to use named pipes for local connections on NT and TCP/IP for all other cases if the client has TCP/IP installed. The host name specifies which protocol is used: *protocol* NULL (none) On NT, try named pipes first; if that doesn't work, use TCP/IP. On Win95/Win98, TCP/IP is used. . Named pipes localhost TCP/IP to current host hostname TCP/IP *Host name* You can force a *MySQL* client to use named pipes by specifying the `--pipe' option. Use the `--socket' option to specify the name of the pipe. You can test whether or not *MySQL* is working by executing the following commands: C:\mysql\bin\mysqlshow C:\mysql\bin\mysqlshow -u root mysql C:\mysql\bin\mysqladmin version status proc C:\mysql\bin\mysql test By default, *MySQL*-Win32 is configured to be installed in `C:\mysql'. If you want to install *MySQL* elsewhere, install it in `C:\mysql', then move the installation to where you want it. If you do move *MySQL*, you must tell `mysqld' where everything is by supplying options to `mysqld'. Use `C:\mysql\bin\mysqld --help' to display all options! For example, if you have moved the *MySQL* distribution to `D:\programs\mysql', you must start `mysqld' with: `D:\programs\mysql\bin\mysqld --basedir D:\programs\mysql' With the registered version of *MySQL*, you can also create a `C:\my.cnf' file that holds any default options for the *MySQL* server. Copy the file `\mysql\my-example.cnf' to `C:\my.cnf' and edit this to suit your setup. Note that you should specify all paths with `/' instead of `\'. If you use `\', you need to specify this twice, as `\' is the escape character in *MySQL*. *Note Option files::. If `mysqld' is slow to answer to connections on Win95/Win98, there is probably a problem with your DNS. In this case, start `mysqld' with `--skip-name-resolve' and use only `localhost' and IP numbers in the *MySQL* grant tables. You can also avoid DNS when connecting to a `mysqld-nt' *MySQL* server running on NT by using the `--pipe' argument to specify use of named pipes. This works for most *MySQL* clients. There are two versions of the *MySQL* command line tool: `mysql' Compiled on native Win32, which offers very limited text editing capabilities. `mysqlc' Compiled with the Cygnus GNU compiler and libraries, which offers `readline' editing. If you want to use `mysqlc.exe', you must copy `C:\mysql\lib\cygwinb19.dll' to `\windows\system' (or similar place). The default privileges on Win32 give all local users full privileges to all databases. To make *MySQL* more secure, you should set a password for all users and remove the row in the `mysql.user' table that has `Host='localhost'' and `User='''. You should also add a password for the `root' user: C:\mysql\bin\mysql mysql mysql> DELETE FROM user WHERE Host='localhost' AND User=''; mysql> QUIT C:\mysql\bin\mysqladmin reload C:\mysql\bin\mysqladmin -u root password your_password After you've set the password, if you want to take down the `mysqld' server, you can do so using this command: mysqladmin --user=root --password=your_password shutdown Connecting to a remote MySQL from Win32 with SSH ------------------------------------------------ Here is a note about how to connect to get a secure connection to remote MySQL server with SSH (by David Carlson). * Install SSH client on your windows machine - I used a free SSH client from `http://www.doc.ic.ac.uk/~ci2/ssh/'. Other useful links: `http://www.npaci.edu/Security/npaci_security_software.html' and `http://www.npaci.edu/Security/samples/ssh32_windows/index.html'. * Start SSH. Set Host Name = yourmysqlserver name or IP address. Set userid=your userid to log in to your server * Click on "local forwards". Set `local port: 3306', `host: localhost', `remote port: 3306' * Save everything, otherwise you'll have to redo it the next time. * Log in to your server with SSH. * Start some ODBC application (for example Access) * Create a new file and link to mySQL using the ODBC driver the same way you normally do except for server, user "localhost". That's it. It works very well with a direct Internet connection. I'm having problems with SSH conflicting with my Win95 network and Wingate - but that'll be the topic of a posting on another software company's usegroup! MySQL-Win32 compared to Unix MySQL ---------------------------------- *MySQL*-Win32 has by now proven itself to be very stable. This version of *MySQL* has the same features as the corresponding Unix version with the following exceptions: *Win95 and threads* Win95 leaks about 200 bytes of main memory for each thread creation. Because of this, you shouldn't run `mysqld' for an extended time on Win95 if you do many connections, since each connection in *MySQL* creates a new thread! WinNT and Win98 don't suffer from this bug. *Blocking read* *MySQL* uses a blocking read for each connection. This means that: * A connection will not be disconnected automatically after 8 hours, as happens with the Unix version of *MySQL*. * If a connection "hangs," it's impossible to break it without killing *MySQL*. * `mysqladmin kill' will not work on a sleeping connection. * `mysqladmin shutdown' can't abort as long as there are sleeping connections. We plan to fix this in the near future. *UDF functions* For the moment, *MySQL*-Win32 does not support user definable functions. *`DROP DATABASE'* You can't drop a database that is in use by some thread. *Killing *MySQL* from the task manager* You can't kill *MySQL* from the task manager or with the shutdown utility in Windows95. You must take it down with `mysqladmin shutdown'. *Case-insensitive names* Filenames are case insensitive on Win32, so database and table names are also case insensitive in *MySQL* for Win32. The only restriction is that database and table names must be given in the same case throughout a given statement. The following query would not work because it refers to a table both as `my_table' and as `MY_TABLE': SELECT * FROM my_table WHERE MY_TABLE.col=1; *The `\' directory character* Pathname components in Win95 are separated by `\' characters, which is also the escape character in *MySQL*. If you are using `LOAD DATA INFILE' or `SELECT ... INTO OUTFILE', you must double the `\' character or use Unix style filenames `/' characters: LOAD DATA INFILE "C:\\tmp\\skr.txt" INTO TABLE skr; SELECT * FROM skr INTO OUTFILE 'C:/tmp/skr.txt'; *`Can't open named pipe' error* If you use the shareware version of *MySQL*-Win32 on NT with the newest mysql-clients you will get the following error: error 2017: can't open named pipe to host: . pipe... This is because the release version of *MySQL* uses named pipes on NT by default. You can avoid this error by using the `--host=localhost' option to the new *MySQL* clients or create a file `C:\my.cnf' that contains the following information: [client] host = localhost *`Access denied for user' error* If you get the error `Access denied for user: 'some-user@unknown' to database 'mysql'' when accessing a *MySQL* server on the same machine, this means that *MySQL* can't resolve your host name properly. To fix this, you should create a file `\windows\hosts' with the following information: 127.0.0.1 localhost Here are some open issues for anyone who might want to help us with the Win32 release: * Make a single user `MYSQL.DLL' server. This should include everything in a standard *MySQL* server, except thread creation. This will make *MySQL* much easier to use in applications that don't need a true client/server and don't need to access the server from other hosts. * Add some nice "start" and "shutdown" icons to the *MySQL* installation. * Create a tool to manage registry entries for the *MySQL* startup options. The registry entry reading is already coded into `mysqld.cc', but it should be recoded to be more "parameter" oriented. The tool should also be able to update the `\my.cnf' file if the user would prefer to use this instead of the registry. * When registering `mysqld' as a service with `--install' (on NT) it would be nice if you could also add default options on the command line. For the moment, the workaround is to update the `C:\my.cnf' file instead. * When you suspend a laptop running Win95, the `mysqld' daemon doesn't accept new connections when the laptop is resumed. We don't know if this is a problem with Win95, TCP/IP or *MySQL*. * It would be real nice to be able to kill `mysqld' from the task manager. For the moment, you must use `mysqladmin shutdown'. * Port `readline' to Win32 for use in the `mysql' command line tool. * GUI versions of the standard *MySQL* clients (`mysql', `mysqlshow', `mysqladmin', and `mysqldump') would be nice. * It would be nice if the socket "read" and "write" functions in `net.c' were interruptible. This would make it possible to kill open threads with `mysqladmin kill' on Win32. * Documentation of which Windows programs work with *MySQL*-Win32/*MyODBC* and what must be done to get them working. * `mysqld' always starts in the "C" locale and not in the default locale. We would like to have `mysqld' use the current locale for the sort order. * Port `sqlclient' to Win32 (almost done) and add more features to it! * Add more options to MysqlManager. * Change the communication protocol between the server and client to use Windows internal communication instead of sockets and TCP/IP. * Implement UDF functions with `.DLL's. * Add macros to use the faster thread-safe increment/decrement methods provided by Win32. Other Win32-specific issues are described in the `README' file that comes with the *MySQL*-Win32 distribution. OS/2 notes ========== *MySQL* uses quite a few open files. Because of this, you should add something like the following to your `CONFIG.SYS' file: SET EMXOPT=-c -n -h1024 If you don't do this, you will probably run into the following error: File 'xxxx' not found (Errcode: 24) When using *MySQL* with OS/2 Warp 3, FixPack 29 or above is required. With OS/2 Warp 4, FixPack 4 or above is required. This is a requirement of the Pthreads library. *MySQL* must be installed in a partition that supports long file names such as HPFS, FAT32, etc. The `INSTALL.CMD' script must be run from OS/2's own `CMD.EXE' and may not work with replacement shells such as `4OS2.EXE'. The `scripts/mysql-install-db' script has been renamed: it is now called `install.cmd' and is a REXX script which will set up the default *MySQL* security settings and create the WorkPlace Shell icons for *MySQL*. Dynamic module support is compiled in but not fully tested. Dynamic modules should be compiled using the Pthreads runtime library. gcc -Zdll -Zmt -Zcrtdll=pthrdrtl -I../include -I../regex -I.. \ -o example udf_example.cc -L../lib -lmysqlclient udf_example.def mv example.dll example.udf *Note:* Due to limitations in OS/2, UDF module name stems must not exceed 8 characters. Modules are stored in the `/mysql2/udf' directory; the `safe-mysqld.cmd' script will put this directory in the `BEGINLIBPATH' environment variable. When using UDF modules, specified extensions are ignored -- it is assumed to be `.udf'. For example, in Unix, the shared module might be named `example.so' and you would load a function from it like this: CREATE FUNCTION metaphon RETURNS STRING SONAME "example.so"; Is OS/2, the module would be named `example.udf', but you would not specify the module extension: CREATE FUNCTION metaphon RETURNS STRING SONAME "example"; TcX binaries ============ As a service, TcX provides a set of binary distributions of *MySQL* that are compiled at TcX or at sites where customers kindly have given us access to their machines. These distributions are generated with `scripts/make_binary_distribution' and are configured with the following compilers and options: SunOS 4.1.4 2 sun4c with `gcc' 2.7.2.1 `CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql --disable-shared' SunOS 5.5.1 sun4u with `egcs' 1.0.3a `CC=gcc CFLAGS="-O6 -fomit-frame-pointer" CXX=gcc CXXFLAGS="-O6 -fomit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-low-memory' SunOS 5.6 sun4u with `egcs' 2.90.27 `CC=gcc CFLAGS="-O6 -fomit-frame-pointer" CXX=gcc CXXFLAGS="-O6 -fomit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-low-memory' SunOS 5.6 i86pc with `gcc' 2.8.1 `CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql --with-low-memory' Linux 2.0.33 i386 with `pgcc' 2.90.29 (`egcs' 1.0.3a) `CFLAGS="-O6 -mpentium -mstack-align-double -fomit-frame-pointer" CXX=gcc CXXFLAGS="-O6 -mpentium -mstack-align-double -fomit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --enable-assembler --with-mysqld-ldflags=-all-static' SCO 3.2v5.0.4 i386 with `gcc' 2.7-95q4 `CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql' AIX 2 4 with `gcc' 2.7.2.2 `CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql' OSF1 V4.0 564 alpha with `gcc' 2.8.1 `CC=gcc CFLAGS=-O CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql --with-low-memory' Irix 6.3 IP32 with `gcc' 2.8.0 `CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql' BSDI BSD/OS 3.1 i386 with `gcc' 2.7.2.1 `CC=gcc CXX=gcc CXXFLAGS=-O ./configure --prefix=/usr/local/mysql' BSDI BSD/OS 2.1 i386 with `gcc' 2.7.2 `CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql' Anyone who has more optimal options for any of the configurations listed above can always mail them to the developer's mailing list at . RPM distributions prior to *MySQL* 3.22 are user-contributed. Beginning with 3.22, some RPMs are TcX-generated. Post-installation setup and testing =================================== Once you've installed *MySQL* (from either a binary or source distribution), you need to initialize the grant tables, start the server and make sure that the server works okay. You may also wish to arrange for the server to be started and stopped automatically when your system starts up and shuts down. Normally you install the grant tables and start the server like this for installation from a source distribution: shell> ./scripts/mysql_install_db shell> cd mysql_installation_directory shell> ./bin/safe_mysqld & For a binary distribution, do this: shell> cd mysql_installation_directory shell> ./bin/mysql_install_db shell> ./bin/safe_mysqld & Testing is most easily done from the top-level directory of the *MySQL* distribution. For a binary distribution, this is your installation directory (typically something like `/usr/local/mysql'). For a source distribution, this is the main directory of your *MySQL* source tree. In the commands shown below in this section and in the following subsections, `BINDIR' is the path to the location in which programs like `mysqladmin' and `safe_mysqld' are installed. For a binary distribution, this is the `bin' directory within the distribution. For a source distribution, `BINDIR' is probably `/usr/local/bin', unless you specified an installation directory other than `/usr/local' when you ran `configure'. `EXECDIR' is the location in which the `mysqld' server is installed. For a binary distribution, this is the same as `BINDIR'. For a source distribution, `EXECDIR' is probably `/usr/local/libexec'. Testing is described in detail below: 1. If necessary, start the `mysqld' server and set up the initial *MySQL* grant tables containing the privileges that determine how users are allowed to connect to the server. This is normally done with the `mysql_install_db' script: shell> scripts/mysql_install_db Typically, `mysql_install_db' needs to be run only the first time you install *MySQL*. Therefore, if you are upgrading an existing installation, you can skip this step. (However, `mysql_install_db' is quite safe to use and will not update any tables that already exist, so if you are unsure what to do, you can always run `mysql_install_db'.) `mysql_install_db' creates six tables (`user', `db', `host', `tables_priv', `columns_priv' and `func') in the `mysql' database. A description of the initial privileges is given in *Note Default privileges::. Briefly, these privileges allow the *MySQL* `root' user to do anything, and allow anybody to create or use databases with a name of `'test'' or starting with `'test_''. If you don't set up the grant tables, the following error will appear in the log file when you start the server: mysqld: Can't find file: 'host.frm' The above may also happens with a binary *MySQL* distribution if you don't start *MySQL* by executing exactly `./bin/safe_mysqld'! You might need to run `mysql_install_db' as `root'. However, if you prefer, you can run the *MySQL* server as an unprivileged (non-`root') user, provided that user can read and write files in the database directory. Instructions for running *MySQL* as an unprivileged user are given in *Note Changing *MySQL* user: Changing MySQL user. If you have problems with `mysql_install_db', see *Note `mysql_install_db': mysql_install_db. There are some alternatives to running the `mysql_install_db' script as it is provided in the *MySQL* distribution: * You may want to edit `mysql_install_db' before running it, to change the initial privileges that are installed into the grant tables. This is useful if you want to install *MySQL* on a lot of machines with the same privileges. In this case you probably should need only to add a few extra `INSERT' statements to the `mysql.user' and `mysql.db' tables! * If you want to change things in the grant tables after installing them, you can run `mysql_install_db', then use `mysql -u root mysql' to connect to the grant tables as the *MySQL* `root' user and issue SQL statements to modify the grant tables directly. * It is possible to recreate the grant tables completely after they have already been created. You might want to do this if you've already installed the tables but then want to recreate them after editing `mysql_install_db'. For more information about these alternatives, see *Note Default privileges::. 2. Start the *MySQL* server like this: shell> cd mysql_installation_directory shell> bin/safe_mysqld & If you have problems starting the server, see *Note Starting server::. 3. Use `mysqladmin' to verify that the server is running. The following commands provide a simple test to check that the server is up and responding to connections: shell> BINDIR/mysqladmin version shell> BINDIR/mysqladmin variables The output from `mysqladmin version' varies slightly depending on your platform and version of *MySQL*, but should be similar to that shown below: shell> BINDIR/mysqladmin version mysqladmin Ver 6.3 Distrib 3.22.9-beta, for pc-linux-gnu on i686 TCX Datakonsult AB, by Monty Server version 3.22.9-beta Protocol version 10 Connection Localhost via UNIX socket TCP port 3306 UNIX socket /tmp/mysql.sock Uptime: 16 sec Running threads: 1 Questions: 20 Reloads: 2 Open tables: 3 To get a feeling for what else you can do with `BINDIR/mysqladmin', invoke it with the `--help' option. 4. Verify that you can shut down the server: shell> BINDIR/mysqladmin -u root shutdown 5. Verify that you can restart the server. Do this using `safe_mysqld' or by invoking `mysqld' directly. For example: shell> BINDIR/safe_mysqld --log & If `safe_mysqld' fails, try running it from the *MySQL* installation directory (if you are not already there). If that doesn't work, see *Note Starting server::. 6. Run some simple tests to verify that the server is working. The output should be similar to what is shown below: shell> BINDIR/mysqlshow +-----------+ | Databases | +-----------+ | mysql | +-----------+ shell> BINDIR/mysqlshow mysql Database: mysql +--------------+ | Tables | +--------------+ | columns_priv | | db | | func | | host | | tables_priv | | user | +--------------+ shell> BINDIR/mysql -e "select host,db,user from db" mysql +------+--------+------+ | host | db | user | +------+--------+------+ | % | test | | | % | test_% | | +------+--------+------+ There is also a benchmark suite in the `sql-bench' directory (under the *MySQL* installation directory) that you can use to compare how *MySQL* performs on different platforms. The `sql-bench/Results' directory contains the results from many runs against different databases and platforms. To run all tests, execute these commands: shell> cd sql-bench shell> run-all-tests If you don't have the `sql-bench' directory, you are probably using an RPM for a binary distribution. (Source distribution RPMs include the benchmark directory.) In this case, you must first install the benchmark suite before you can use it. Beginning with *MySQL* 3.22, there are benchmark RPM files named `mysql-bench-VERSION-i386.rpm' that contain benchmark code and data. If you have a source distribution, you can also run the tests in the `tests' subdirectory. For example, to run `auto_increment.tst', do this: shell> BINDIR/mysql -vvf test < ./tests/auto_increment.tst The expected results are shown in the `./tests/auto_increment.res' file. Problems running `mysql_install_db' ----------------------------------- This section lists problems you might encounter when you run `mysql_install_db': *`mysql_install_db' doesn't install the grant tables* You may find that `mysql_install_db' fails to install the grant tables and terminates after displaying the following messages: starting mysqld daemon with databases from XXXXXX mysql daemon ended In this case, you should examine the log file very carefully! The log should be located in the directory `XXXXXX' named by the error message, and should indicate why `mysqld' didn't start. If you don't understand what happened, include the log when you post a bug report using `mysqlbug'! *Note Bug reports::. *There is already a `mysqld' daemon running* In this case, you have probably don't have to run `mysql_install_db' at all. You have to run `mysql_install_db' only once, when you install *MySQL* the first time. *Installing a second `mysqld' daemon doesn't work when one daemon is running* This can happen when you already have an existing *MySQL* installation, but want to put a new installation in a different place (e.g., for testing, or perhaps you simply want to run two installations at the same time). Generally the problem that occurs when you try to run the second server is that it tries to use the same socket and port as the old one. In this case you will get the error message: `Can't start server: Bind on TCP/IP port: Address already in use' or `Can't start server : Bind on unix socket...' You can start the new server with a different socket and port as follows: shell> MYSQL_UNIX_PORT=/tmp/mysqld-new.sock shell> MYSQL_TCP_PORT=3307 shell> export MYSQL_UNIX_PORT MYSQL_TCP_PORT shell> scripts/mysql_install_db shell> bin/safe_mysqld & After this, you should edit your server boot script to start both daemons with different sockets and ports. For example, it could invoke `safe_mysqld' twice, but with different `--socket', `--port' and `--basedir' options for each invocation. *You don't have write access to `/tmp'* If you don't have write access to create a socket file at the default place (in `/tmp') or permission to create temporary files in `/tmp,' you will get an error when running `mysql_install_db' or when starting or using `mysqld'. You can specify a different socket and temporary directory as follows: shell> TMPDIR=/some_tmp_dir/ shell> MYSQL_UNIX_PORT=/some_tmp_dir/mysqld.sock shell> export TMPDIR MYSQL_UNIX_PORT `some_tmp_dir' should be the path to some directory for which you have write permission. After this you should be able to run `mysql_install_db' and start the server with these commands: shell> scripts/mysql_install_db shell> BINDIR/safe_mysqld & *`mysqld' crashes immediately* If you are running RedHat 5.0 with a version of `glibc' older than 2.0.7-5, you should make sure you have installed all `glibc' patches! There is a lot of information about this in the *MySQL* mail archives. Links to the mail archives are available at the online *MySQL* documentation page (http://www.mysql.com/doc.html). Also, see *Note Linux::. You can also start `mysqld' manually using the `--skip-grant' option and add the privilege information yourself using `mysql': shell> BINDIR/safe_mysqld --skip-grant & shell> BINDIR/mysql -u root mysql From `mysql', manually execute the SQL commands in `mysql_install_db'. Make sure you run `mysqladmin reload' afterward to tell the server to reload the grant tables. Problems starting the MySQL server ---------------------------------- Generally, you start the `mysqld' server in one of three ways: * By invoking `mysql.server'. This script is used primarily at system startup and shutdown, and is described more fully in *Note Automatic start::. * By invoking `safe_mysqld', which tries to determine the proper options for `mysqld' and then runs it with those options. * By invoking `mysqld' directly. Whichever method you use to start the server, if it fails to start up correctly, check the log file to see if you can find out why. Log files are located in the data directory (typically `/usr/local/mysql/data' for a binary distribution, `/usr/local/var' for a source distribution). Look in the data directory for files with names of the form `host_name.err' and `host_name.log' where `host_name' is the name of your server host. Then check the last few lines of these files: shell> tail host_name.err shell> tail host_name.log When the `mysqld' daemon starts up, it changes directory to the data directory. This is where it expects to write log files and the pid (process ID) file, and where it expects to find databases. The data directory location is hardwired in when the distribution is compiled. However, if `mysqld' expects to find the data directory somewhere other than where it really is on your system, it will not work properly. If you have problems with incorrect paths, you can find out what options `mysqld' allows and what the default path settings are by invoking `mysqld' with the `--help' option. You can override the defaults by specifying the correct pathnames as command-line arguments to `mysqld'. (These options can be used with `safe_mysqld' as well.) Normally you should need to tell `mysqld' only the base directory under which *MySQL* is installed. You can do this with the `--basedir' option. You can also use `--help' to check the effect of changing path options (note that `--help' *must* be the final option of the `mysqld' command). For example: shell> EXECDIR/mysqld --basedir=/usr/local --help Once you determine the path settings you want, start the server without the `--help' option. If you get the following error, it means that some other program (or another `mysqld' server) is already using the TCP/IP port or socket `mysqld' is trying to use: Can't start server: Bind on TCP/IP port: Address already in use or Can't start server : Bind on unix socket... Use `ps' to make sure that you don't have another `mysqld' server running. If you can't find another server running, you can try to execute the command `telnet your-host-name tcp-ip-port-number' and press `RETURN' a couple of times. If you don't get a error message like `telnet: Unable to connect to remote host: Connection refused', something is using the TCP/IP port `mysqld' is trying to use. *Note `mysql_install_db': mysql_install_db, and *Note Multiple servers::. The `safe_mysqld' script is written so that it normally is able to start a server that was installed from either a source or a binary version of *MySQL*, even if these install the server in slightly different locations. `safe_mysqld' expects one of these conditions to be true: * The server and databases can be found relative to the directory from which `safe_mysqld' is invoked. `safe_mysqld' looks under its working directory for `bin' and `data' directories (for binary distributions) or for `libexec' and `var' directories (for source distributions). This condition should be met if you execute `safe_mysqld' from your *MySQL* installation directory (for example, `/usr/local/mysql' for a binary distribution). * If the server and databases cannot be found relative to its working directory, `safe_mysqld' attempts to locate them by absolute pathnames. Typical locations are `/usr/local/libexec' and `/usr/local/var'. The actual locations are determined when the distribution was built from which `safe_mysqld' comes. They should be correct if *MySQL* was installed in a standard location. Since `safe_mysqld' will try to find the server and databases relative to its own working directory, you can install a binary distribution of *MySQL* anywhere, as long as you start `safe_mysqld' from the *MySQL* installation directory: shell> cd mysql_installation_directory shell> bin/safe_mysqld & If `safe_mysqld' fails, even when invoked from the *MySQL* installation directory, you can modify it to use the path to `mysqld' and the pathname options that are correct for your system. Note that if you upgrade *MySQL* in the future, your modified version of `safe_mysqld' will be overwritten, so you should make a copy of your edited version that you can reinstall. If `mysqld' is currently running, you can find out what path settings it is using by executing this command: shell> mysqladmin variables or shell> mysqladmin -h 'your-host-name' variables If `safe_mysqld' starts the server but you can't connect to it, you should make sure you have an entry in `/etc/hosts' that looks like this: 127.0.0.1 localhost This problem occurs only on systems that don't have a working thread library and for which *MySQL* must be configured to use MIT-pthreads. Starting and stopping MySQL automatically ----------------------------------------- The `mysql.server' script can be used to start or stop the server, by invoking it with `start' or `stop' arguments: shell> mysql.server start shell> mysql.server stop `mysql.server' can be found in the `share/mysql' directory under the *MySQL* installation directory, or in the `support-files' directory of the *MySQL* source tree. Before `mysql.server' starts the server, it changes directory to the *MySQL* installation directory, then invokes `safe_mysqld'. You might need to edit `mysql.server' if you have a binary distribution that you've installed in a non-standard location. Modify it to `cd' into the proper directory before it runs `safe_mysqld'. If you want the server to run as some specific user, you can change the `mysql_daemon_user=root' line to use another user. You can also modify `mysql.server' to pass other options to `safe_mysqld'. `mysql.server stop' brings down server by sending a signal to it. You can take down the server manually by executing `mysqladmin shutdown'. You might want to add these start and stop commands to the appropriate places in your `/etc/rc*' files when you start using *MySQL* for production applications. Note that if you modify `mysql.server', then if you upgrade *MySQL* sometime, your modified version will be overwritten, so you should make a copy of your edited version that you can reinstall. If your system uses `/etc/rc.local' to start external scripts, you should append the following to it: /bin/sh -c 'cd /usr/local/mysql ; ./bin/safe_mysqld &' You can also add options for `mysql.server' in a global `/etc/my.cnf' file. A typical `/etc/my.cnf' file might look like this: [mysqld] datadir=/usr/local/mysql/var socket=/tmp/mysqld.sock port=3306 [mysql.server] user=mysql basedir=/usr/local/mysql The `mysql.server' script uses the following variables: `user', `datadir', `basedir', `bindir' and `pid-file'. *Note Option files::. Option files ------------ *MySQL* 3.22 can read default startup options for the server and for clients from option files. *MySQL* reads default options from the following files on Unix: *Filename* *Purpose* `/etc/my.cnf' Global options `DATADIR/my.cnf' Server-specific options `~/.my.cnf' User-specific options `DATADIR' is the *MySQL* data directory (typically `/usr/local/mysql/data' for a binary installation, or `/usr/local/var' for a source installation). Note that this is the directory that was specified at configuration time, not the one specified with `--datadir' when `mysqld' starts up! (`--datadir' has no effect on where the server looks for option files, because it looks for them before it processes any command-line arguments.) *MySQL* reads default options from the following files on Win32: *Filename* *Purpose* `windows-system-directory\my.ini' `C:\my.cnf' Global options `C:\mysql\data\my.cnf' Server-specific options Note that you on Win32 should specify all paths with `/' instead of `\'. If you use `\', you need to specify this twice, as `\' is the escape character in *MySQL*. *MySQL* tries to read option files in the order listed above. If multiple option files exist, an option specified in a file read later takes precedence over the same option specified in a file read earlier. Options specified on the command line take precedence over options specified in any option file. Some options can be specified using environment variables. Options specified on the command line or in option files take precedence over environment variable values. The following programs support option files: `mysql', `mysqladmin', `mysqld', `mysqldump', `mysqlimport', `mysql.server', `isamchk' and `pack_isam'. You can use option files to specify any long option that a program supports! Run the program with `--help' to get a list of available options. An option file can contain lines of the following forms: `#comment' Comment lines start with `#' or `;'. Empty lines are ignored. `[group]' `group' is the name of the program or group for which you want to set options. After a group line, any `option' or `set-variable' lines apply to the named group until the end of the option file or another group line is given. `option' This is equivalent to `--option' on the command line. `option=value' This is equivalent to `--option=value' on the command line. `set-variable = variable=value' This is equivalent to `--set-variable variable=value' on the command line. This syntax must be used to set a `mysqld' variable. The `client' group allows you to specify options that apply to all *MySQL* clients (not `mysqld'). This is the perfect group to use to specify the password you use to connect to the server. (But make sure the option file is readable and writable only to yourself.) Note that for options and values, all leading and trailing blanks are automatically deleted. You may use the escape sequences `\b', `\t', `\n', `\r', `\\' and `\s' in your value string (`\s' == blank). Here is a typical global option file: [client] port=3306 socket=/tmp/mysql.sock [mysqld] port=3306 socket=/tmp/mysql.sock set-variable = key_buffer=16M set-variable = max_allowed_packet=1M [mysqldump] quick Here is typical user option file: [client] # The following password will be sent to all standard MySQL clients password=my_password [mysql] no-auto-rehash If you have a source distribution, you will find a sample configuration file named `my-example.cnf' in the `support-files' directory. If you have a binary distribution, look in the `DIR/share/mysql' directory, where `DIR' is the pathname to the *MySQL* installation directory (typically `/usr/local/mysql'). You can copy `my-example.cnf' to your home directory (rename the copy to `.my.cnf') to experiment with. To tell a *MySQL* program not to read any option files, specify `--no-defaults' as the first option on the command line. This *MUST* be the first option or it will have no effect! If you want to check which options are used, you can give the option `--print-defaults' as the first option. If you want to force the use of a specific config file, you can use the option `--defaults-file=full-path-to-default-file'. If you do this, only the specified file will be read. Note for developers: Option file handling is implemented simply by processing all matching options (i.e., options in the appropriate group) before any command line arguments. This works nicely for programs that use the last instance of an option that is specified multiple times. If you have an old program that handles multiply-specified options this way but doesn't read option files, you need add only two lines to give it that capability. Check the source code of any of the standard *MySQL* clients to see how to do this. Is there anything special to do when upgrading/downgrading MySQL? ================================================================= You can always move the *MySQL* form and data files between different versions on the same architecture as long as you have the same base version of *MySQL*. The current base version is 3. If you change the character set by recompiling *MySQL* (which may also change the sort order), you must run `isamchk -r -q' on all tables. Otherwise your indexes may not be ordered correctly. If you are paranoid and/or afraid of new versions, you can always rename your old `mysqld' to something like `mysqld'-'old-version-number'. If your new `mysqld' then does something unexpected, you can simply shut it down and restart with your old `mysqld'! When you do an upgrade you should also backup your old databases, of course. Sometimes it's good to be a little paranoid! After an upgrade, if you experience problems with recompiled client programs, like `Commands out of sync' or unexpected core dumps, you probably have used an old header or library file when compiling your programs. In this case you should check the date for your `mysql.h' file and `libmysqlclient.a' library to verify that they are from the new *MySQL* distribution. If not, please recompile your programs! If you get some problems that the new `mysqld' server doesn't want to start or that you can't connect without a password, check that you don't have some old `my.cnf' file from your old installation! You can check this with: `program-name --print-defaults'. If this outputs anything other than the program name, you have a active `my.cnf' file that will may affect things! It is a good idea to rebuild and reinstall the `Msql-Mysql-modules' distribution whenever you install a new release of *MySQL*, particularly if you notice symptoms such as all your `DBI' scripts dumping core after you upgrade *MySQL*. Upgrading from a 3.22 version to 3.23 ------------------------------------- *MySQL* 3.23 supports tables of the new `MyISAM' type and the old `NISAM' type. You don't have to convert your old tables to use these with 3.23. By default, all new tables will be created with type `MyISAM' (unless you start `mysqld' with the `--default-table-type=isam' option. You can change an `ISAM' table to a `MyISAM' table with `ALTER TABLE' or the Perl script `mysql_convert_table_format'. 3.22 and 3.21 clients will work without any problems with a 3.23 server. The following lists what you have to watch out for when upgrading to 3.23: * `INNER' and `DELAYED' are now reserved words. * `FLOAT(4)' and `FLOAT(8)' are now true floating point types. * When declaring `DECIMAL(length,dec)' the length argument no longer includes a place for the sign or the decimal point. * A `TIME' string must now be of one of the following formats: `[[[DAYS] [H]H:]MM:]SS[.fraction]' or `[[[[[H]H]H]H]MM]SS[.fraction]' * `LIKE' now compares strings using the same character comparison rules as `'=''. If you require the old behavior, you can compile *MySQL* with the `CXXFLAGS=-DLIKE_CMP_TOUPPER' flag. * `REGEXP' is now case insensitive for normal (not binary) strings. * When you check/repair tables you should use `myisamchk' for `MyISAM' tables (`.MYI') and `isamchk' for ISAM (`.ISM') tables. * If you want your `mysqldump's to be compatible between *MySQL* 3.22 and 3.23, you should not use the `--opt' or `--full' option to `mysqldump'. * Check all your calls to `DATE_FORMAT()' to make sure there is a `%' before each format character. * `mysql_fetch_fields_direct' is now a function (it was a macro) and it returns a pointer to a `MYSQL_FIELD' instead of a `MYSQL_FIELD'. * `mysql_num_fields()' can no longer be used on a `MYSQL*' object (it's now a function that takes `MYSQL_RES*' as an argument. You should now use `mysql_field_count()' instead. * In `MySQL' 3.22, the output of `SELECT DISTINCT ...' was almost always sorted. In 3.23, you must use `GROUP BY' or `ORDER BY' to obtain sorted output. * `SUM()' now returns `NULL', instead of 0, if there is no matching rows. This is according to ANSI SQL. * New restricted words: `CASE, THEN, WHEN, ELSE and END' Upgrading from a 3.21 version to 3.22 ------------------------------------- Nothing that affects compatibility has changed between 3.21 and 3.22. The only pitfall is that new tables that are created with `DATE' type columns will use the new way to store the date. You can't access these new fields from an old version of `mysqld'. After installing *MySQL* 3.22, you should start the new server and then run the `mysql_fix_privilege_tables' script. This will add the new privileges that you need to use the `GRANT' command. If you forget this, you will get `Access denied' when you try to use `ALTER TABLE', `CREATE INDEX' or `DROP INDEX'. If your *MySQL* root user requires a password, you should give this as an argument to `mysql_fix_privilege_tables'. The C API interface to `mysql_real_connect()' has changed. If you have an old client program that calls this function, you must place a `0' for the new `db' argument (or recode the client to send the `db' element for faster connections). You must also call `mysql_init()' before calling `mysql_real_connect()'! This change was done to allow the new `mysql_options()' function to save options in the `MYSQL' handler structure. Upgrading from a 3.20 version to 3.21 ------------------------------------- If you are running a version older than 3.20.28 and want to switch to 3.21.x, you need to do the following: You can start the `mysqld' 3.21 server with `safe_mysqld --old-protocol' to use it with clients from the 3.20 distribution. In this case, the new client function `mysql_errno()' will not return any server error, only `CR_UNKNOWN_ERROR', (but it works for client errors) and the server uses the old password() checking rather than the new one. If you are *NOT* using the `--old-protocol' option to `mysqld', you will need to make the following changes: * All client code must be recompiled. If you are using ODBC, you must get the new *MyODBC* 2.x driver. * The script `scripts/add_long_password' must be run to convert the `Password' field in the `mysql.user' table to `CHAR(16)'. * All passwords must be reassigned in the `mysql.user' table (to get 62-bit rather than 31-bit passwords). * The table format hasn't changed, so you don't have to convert any tables. *MySQL* 3.20.28 and above can handle the new `user' table format without affecting clients. If you have a *MySQL* version earlier than 3.20.28, passwords will no longer work with it if you convert the `user' table. So to be safe, you should first upgrade to at least 3.20.28 and then upgrade to 3.21.x. The new client code works with a 3.20.x `mysqld' server, so if you experience problems with 3.21.x, you can use the old 3.20.x server without having to recompile the clients again. If you are not using the `--old-protocol' option to `mysqld', old clients will issue the error message: ERROR: Protocol mismatch. Server Version = 10 Client Version = 9 The new Perl `DBI'/`DBD' interface also supports the old `mysqlperl' interface. The only change you have to make if you use `mysqlperl' is to change the arguments to the `connect()' function. The new arguments are: `host', `database', `user', `password' (the `user' and `password' arguments have changed places). *Note Perl `DBI' Class: Perl DBI Class. The following changes may affect queries in old applications: * `HAVING' must now be specified before any `ORDER BY' clause. * The parameters to `LOCATE()' have been swapped. * There are some new reserved words. The most notable are `DATE', `TIME' and `TIMESTAMP'. Upgrading to another architecture --------------------------------- If you are using *MySQL* 3.23, you can copy the `.frm', the `.MYI' and the `.MYD' files between different architectures that support the same floating point format. (*MySQL* takes care of any byte swapping issues). The *MySQL* data `*.ISD' and the index files `*.ISM' files) are architecture-dependent and in some case OS-dependent. If you want to move your applications to another machine that has a different architecture or OS than your current machine, you should not try to move a database by simply copying the files to the other machine. Use `mysqldump' instead. By default, `mysqldump' will create a file full of SQL statements. You can then transfer the file to the other machine and feed it as input to the `mysql' client. Try `mysqldump --help' to see what options are available. If you are moving the data to a newer version of *MySQL*, you should use `mysqldump --opt' with the newer version to get a fast, compact dump. The easiest (although not the fastest) way to move a database between two machines is to run the following commands on the machine on which the database is located: shell> mysqladmin -h 'other hostname' create db_name shell> mysqldump --opt db_name \ | mysql -h 'other hostname' db_name If you want to copy a database from a remote machine over a slow network, you can use: shell> mysqladmin create db_name shell> mysqldump -h 'other hostname' --opt --compress db_name \ | mysql db_name You can also store the result in a file, then transfer the file to the target machine and load the file into the database there. For example, you can dump a database to a file on the source machine like this: shell> mysqldump --quick db_name | gzip > db_name.contents.gz (The file created in this example is compressed.) Transfer the file containing the database contents to the target machine and run these commands there: shell> mysqladmin create db_name shell> gunzip < db_name.contents.gz | mysql db_name You can also use `mysqldump' and `mysqlimport' to accomplish the database transfer. For big tables, this is much faster than simply using `mysqldump'. In the commands shown below, `DUMPDIR' represents the full pathname of the directory you use to store the output from `mysqldump'. First, create the directory for the output files and dump the database: shell> mkdir DUMPDIR shell> mysqldump --tab=DUMPDIR db_name Then transfer the files in the `DUMPDIR' directory to some corresponding directory on the target machine and load the files into *MySQL* there: shell> mysqladmin create db_name # create database shell> cat DUMPDIR/*.sql | mysql db_name # create tables in database shell> mysqlimport db_name DUMPDIR/*.txt # load data into tables Also, don't forget to copy the `mysql' database, since that's where the grant tables (`user', `db', `host') are stored. You may have to run commands as the *MySQL* `root' user on the new machine until you have the `mysql' database in place. After you import the `mysql' database on the new machine, execute `mysqladmin flush-privileges' so that the server reloads the grant table information. How standards-compatible is MySQL? ********************************** MySQL extensions to ANSI SQL92 ============================== *MySQL* includes some extensions that you probably will not find in other SQL databases. Be warned that if you use them, your code will not be portable to other SQL servers. In some cases, you can write code that includes *MySQL* extensions, but is still portable, by using comments of the form `/*! ... */'. In this case, *MySQL* will parse and execute the code within the comment as it would any other *MySQL* statement, but other SQL servers will ignore the extensions. For example: SELECT /*! STRAIGHT_JOIN */ col_name FROM table1,table2 WHERE ... If you add a version number after the `'!'', the syntax will only be executed if the *MySQL* version is equal or newer than the used version number: CREATE /*!32302 TEMPORARY */ TABLE (a int); The above means that if you have 3.23.02 or newer, then *MySQL* will use the `TEMPORARY' keyword. *MySQL* extensions are listed below: * The field types `MEDIUMINT', `SET', `ENUM' and the different `BLOB' and `TEXT' types. * The field attributes `AUTO_INCREMENT', `BINARY', `UNSIGNED' and `ZEROFILL'. * All string comparisons are case insensitive by default, with sort ordering determined by the current character set (ISO-8859-1 Latin1 by default). If you don't like this, you should declare your columns with the `BINARY' attribute or use the `BINARY' cast, which causes comparisons to be done according to the ASCII order used on the *MySQL* server host. * *MySQL* maps each database to a directory under the *MySQL* data directory, and tables within a database to filenames in the database directory. This has two implications: - Database names and table names are case sensitive in *MySQL* on operating systems that have case sensitive filenames (like most Unix systems). If you have a problem remembering table names, adopt a consistent convention, such as always creating databases and tables using lowercase names. - Database, table, index, column or alias names may begin with a digit (but may not consist solely of digits). - You can use standard system commands to backup, rename, move, delete and copy tables. For example, to rename a table, rename the `.ISD', `.ISM' and `.frm' files to which the table corresponds. * In SQL statements, you can access tables from different databases with the `db_name.tbl_name' syntax. Some SQL servers provide the same functionality but call this `User space'. *MySQL* dosen't support tablespaces like in: `create table ralph.my_table...IN my_tablespace'. * `LIKE' is allowed on numeric columns. * Use of `INTO OUTFILE' and `STRAIGHT_JOIN' in a `SELECT' statement. *Note `SELECT': SELECT. * The `SQL_SMALL_RESULT' option in a `SELECT' statement. * `EXPLAIN SELECT' to get a description on how tables are joined. * Use of index names, indexes on a prefix of a field, and use of `INDEX' or `KEY' in a `CREATE TABLE' statement. *Note `CREATE TABLE': CREATE TABLE. * Use of `TEMPORARY' or `IF NOT EXISTS' with `CREATE TABLE'. * Use of `COUNT(DISTINCT list)' where 'list' is more than one element. * Use of `CHANGE col_name', `DROP col_name' or `DROP INDEX' in an `ALTER TABLE' statement. *Note `ALTER TABLE': ALTER TABLE. * Use of `IGNORE' in an `ALTER TABLE' statement. * Use of multiple `ADD', `ALTER', `DROP' or `CHANGE' clauses in an `ALTER TABLE' statement. * Use of `DROP TABLE' with the keywords `IF EXISTS'. * You can drop multiple tables with a single `DROP TABLE' statement. * The `LIMIT' clause of the `DELETE' statement. * The `DELAYED' clause of the `INSERT' and `REPLACE' statements. * The `LOW_PRIORITY' clause of the `INSERT', `REPLACE', `DELETE' and `UPDATE' statements. * Use of `LOAD DATA INFILE'. In many cases, this syntax is compatible with Oracle's `LOAD DATA INFILE'. *Note `LOAD DATA': LOAD DATA. * The `OPTIMIZE TABLE' statement. *Note `OPTIMIZE TABLE': OPTIMIZE TABLE. * The `SHOW' statement. *Note `SHOW': SHOW. * Strings may be enclosed by either `"' or `'', not just by `''. * Use of the escape `\' character. * The `SET OPTION' statement. *Note `SET OPTION': SET OPTION. * You don't need to name all selected columns in the `GROUP BY' part. This gives better performance for some very specific, but quite normal queries. *Note Group by functions::. * To make it easier for users that come from other SQL environments, *MySQL* supports aliases for many functions. For example, all string functions support both ANSI SQL syntax and ODBC syntax. * *MySQL* understands the `||' and `&&' operators to mean logical OR and AND, as in the C programming language. In *MySQL*, `||' and `OR' are synonyms, as are `&&' and `AND'. Because of this nice syntax, *MySQL* doesn't support the ANSI SQL `||' operator for string concatenation; use `CONCAT()' instead. Since `CONCAT()' takes any number of arguments, it's easy to convert use of the `||' operator to *MySQL*. * `CREATE DATABASE' or `DROP DATABASE'. *Note `CREATE DATABASE': CREATE DATABASE. * The `%' operator is a synonym for `MOD()'. That is, `N % M' is equivalent to `MOD(N,M)'. `%' is supported for C programmers and for compatibility with PostgreSQL. * The `=', `<>', `<=' ,`<', `>=',`>', `<<', `>>', `<=>', `AND', `OR' or `LIKE' operators may be used in column comparisons to the left of the `FROM' in `SELECT' statements. For example: mysql> SELECT col1=1 AND col2=2 FROM tbl_name; * The `LAST_INSERT_ID()' function. *Note `mysql_insert_id()': mysql_insert_id. * The `REGEXP' and `NOT REGEXP' extended regular expression operators. * `CONCAT()' or `CHAR()' with one argument or more than two arguments. (In *MySQL*, these functions can take any number of arguments.) * The `BIT_COUNT()', `CASE', `ELT()', `FROM_DAYS()', `FORMAT()', `IF()', `PASSWORD()', `ENCRYPT()', `md5()', `ENCODE()', `DECODE()', `PERIOD_ADD()', `PERIOD_DIFF()', `TO_DAYS()', or `WEEKDAY()' functions. * Use of `TRIM()' to trim substrings. ANSI SQL only supports removal of single characters. * The `GROUP BY' functions `STD()', `BIT_OR()' and `BIT_AND()'. * Use of `REPLACE' instead of `DELETE' + `INSERT'. *Note `REPLACE': REPLACE. * The `FLUSH flush_option' statement. MySQL differences compared to ANSI SQL92 ======================================== We try to make *MySQL* follow the ANSI SQL standard and the ODBC SQL standard, but in some cases *MySQL* does some things differently: * `--' is only a comment if followed by a white space. *Note Missing comments::. * For `VARCHAR' columns, trailing spaces are removed when the value is stored. *Note Bugs::. * In some cases, `CHAR' columns are silently changed to `VARCHAR' columns. *Note Silent column changes::. * Privileges for a table is not automatically revoked when you delete a table. You must explicitly issue a `REVOKE' to revoke privileges for a table. *Note `GRANT': GRANT. Functionality missing from MySQL ================================ The following functionality is missing in the current version of *MySQL*. For a prioritized list indicating when new extensions may be added to *MySQL*, you should consult the online *MySQL* TODO list (http://www.mysql.com/Manual_chapter/manual_Todo.html). That is the latest version of the TODO list in this manual. *Note TODO::. Sub-selects ----------- The following will not yet work in *MySQL*: SELECT * FROM table1 WHERE id IN (SELECT id FROM table2); SELECT * FROM table1 WHERE id NOT IN (SELECT id FROM table2); However, in many cases you can rewrite the query without a sub select: SELECT table1.* FROM table1,table2 WHERE table1.id=table2.id; SELECT table1.* FROM table1 LEFT JOIN table2 ON table1.id=table2.id where table2.id IS NULL For more complicated sub queries you can create temporary tables to hold the sub query. *MySQL* only supports `INSERT ... SELECT ...' and `REPLACE ... SELECT ...' Independent sub-selects will be probably be available in 3.24.0. You can now use the function `IN()' in other contexts, however. `SELECT INTO TABLE' ------------------- *MySQL* doesn't yet support the Oracle SQL extension: `SELECT ... INTO TABLE ...'. *MySQL* supports instead the ANSI SQL syntax `INSERT INTO ... SELECT ...', which is basically the same thing. Alternatively, you can use `SELECT INTO OUTFILE...' or `CREATE TABLE ... SELECT' to solve your problem. Transactions ------------ Transactions are not supported. *MySQL* shortly will support atomic operations, which are like transactions without rollback. With atomic operations, you can execute a group of `INSERT'/`SELECT'/whatever commands and be guaranteed that no other thread will interfere. In this context, you won't usually need rollback. Currently, you can prevent interference from other threads by using the `LOCK TABLES' and `UNLOCK TABLES' commands. *Note `LOCK TABLES': LOCK TABLES. Stored procedures and triggers ------------------------------ A stored procedure is a set of SQL commands that can be compiled and stored in the server. Once this has been done, clients don't need to keep reissuing the entire query but can refer to the stored procedure. This provides better performance because the query has to be parsed only once and less information needs to be sent between the server and the client. You can also raise the conceptual level by having libraries of functions in the server. A trigger is a stored procedure that is invoked when a particular event occurs. For example, you can install a stored procedure that is triggered each time a record is deleted from a transaction table and that automatically deletes the corresponding customer from a customer table when all his transactions are deleted. The planned update language will be able to handle stored procedures, but without triggers. Triggers usually slow down everything, even queries for which they are not needed. To see when *MySQL* might get stored procedures, see *Note TODO::. Foreign Keys ------------ Note that foreign keys in SQL are not used to join tables, but are used mostly for checking referential integrity. If you want to get results from multiple tables from a `SELECT' statement, you do this by joining tables! SELECT * from table1,table2 where table1.id = table2.id; *Note `JOIN': JOIN. *Note example-Foreign keys::. The `FOREIGN KEY' syntax in *MySQL* exists only for compatibility with other SQL vendors' `CREATE TABLE' commands; it doesn't do anything. The `FOREIGN KEY' syntax without `ON DELETE ...' is mostly used for documentation purposes. Some ODBC applications may use this to produce automatic `WHERE' clauses, but this is usually easy to override. `FOREIGN KEY' is sometimes used as a constraint check, but this check is unnecessary in practice if rows are inserted into the tables in the right order. *MySQL* only supports these clauses because some applications require them to exist (regardless of whether or not they work!). In *MySQL*, you can work around the problem of `ON DELETE ...' not being implemented by adding the appropriate `DELETE' statement to an application when you delete records from a table that has a foreign key. In practice this is as quick (in some cases quicker) and much more portable than using foreign keys. In the near future we will extend the `FOREIGN KEY' implementation so that at least the information will be saved in the table specification file and may be retrieved by `mysqldump' and ODBC. Reasons NOT to use foreign keys ............................... There are so many problems with `FOREIGN KEY's that we don't know where to start: * Foreign keys make life very complicated, because the foreign key definitions must be stored in a database and implementing them would destroy the whole "nice approach" of using files that can be moved, copied and removed. * The speed impact is terrible for `INSERT' and `UPDATE' statements, and in this case almost all `FOREIGN KEY' checks are useless because you usually insert records in the right tables in the right order, anyway. * There is also a need to hold locks on many more tables when updating one table, because the side effects can cascade through the entire database. It's MUCH faster to delete records from one table first and subsequently delete them from the other tables. * You can no longer restore a table by doing a full delete from the table and then restoring all records (from a new source or from a backup). * If you have foreign keys you can't dump and restore tables unless you do so in a very specific order. * It's very easy to do "allowed" circular definitions that make the tables impossible to recreate each table with a single create statement, even if the definition works and is usable. The only nice aspect of `FOREIGN KEY' is that it gives ODBC and some other client programs the ability to see how a table is connected and to use this to show connection diagrams and to help in building applicatons. *MySQL* will soon store `FOREIGN KEY' definitions so that a client can ask for and receive an answer how the original connection was made. The current `.frm' file format does not have any place for it. Views ----- *MySQL* doesn't support views, but this is on the TODO. `--' as the start of a comment ------------------------------ Some other SQL databases use `--' to start comments. *MySQL* has `#' as the start comment character, even if the `mysql' command line tool removes all lines that start with `--'. You can also use the C comment style `/* this is a comment */' with *MySQL*. *Note Comments::. *MySQL* 3.23.3 and above supports the `--' comment style only if the comment is followed by a space. This is because this degenerate comment style has caused many problems with automatically generated SQL queries that have used something like the following code, where we automatically insert the value of the payment for `!payment!': UPDATE tbl_name SET credit=credit-!payment! What do you think will happen when the value of `payment' is negative? Because `1--1' is legal in SQL, we think it is terrible that `--' means start comment. In MySQL 3.23 you can however use: `1-- This is a comment' The following discussing only concerns you if you are running an *MySQL* version earlier than 3.23: If you have a SQL program in a text file that contains `--' comments you should use: shell> replace " --" " #" < text-file-with-funny-comments.sql \ | mysql database instead of the usual: shell> mysql database < text-file-with-funny-comments.sql You can also edit the command file "in place" to change the `--' comments to `#' comments: shell> replace " --" " #" -- text-file-with-funny-comments.sql Change them back with this command: shell> replace " #" " --" -- text-file-with-funny-comments.sql What standards does MySQL follow? ================================= Entry level SQL92. ODBC level 0-2. How to cope without `COMMIT'/`ROLLBACK' ======================================= *MySQL* doesn't support `COMMIT'-`ROLLBACK.' The problem is that handling `COMMIT'-`ROLLBACK' efficiently would require a completely different table layout than *MySQL* uses today. *MySQL* would also need extra threads that do automatic cleanups on the tables and the disk usage would be much higher. This would make *MySQL* about 2-4 times slower than it is today. *MySQL* is much faster than almost all other SQL databases (typically at least 2-3 times faster). One of the reasons for this is the lack of `COMMIT'-`ROLLBACK'. For the moment, we are much more for implementing the SQL server language (something like stored procedures). With this you would very seldom really need `COMMIT'-`ROLLBACK.' This would also give much better performance. Loops that need transactions normally can be coded with the help of `LOCK TABLES', and you don't need cursors when you can update records on the fly. We have transactions and cursors on the TODO but not quite prioritized. If we implement these, it will be as an option to `CREATE TABLE'. That means that `COMMIT'-`ROLLBACK' will work only on those tables, so that a speed penalty will be imposed on those table only. We at TcX have a greater need for a real fast database than a 100% general database. Whenever we find a way to implement these features without any speed loss, we will probably do it. For the moment, there are many more important things to do. Check the TODO for how we prioritize things at the moment. (Customers with higher levels of support can alter this, so things may be reprioritized.) The current problem is actually `ROLLBACK'. Without `ROLLBACK', you can do any kind of `COMMIT' action with `LOCK TABLES'. To support `ROLLBACK', *MySQL* would have to be changed to store all old records that were updated and revert everything back to the starting point if `ROLLBACK' was issued. For simple cases, this isn't that hard to do (the current `isamlog' could be used for this purpose), but it would be much more difficult to implement `ROLLBACK' for `ALTER/DROP/CREATE TABLE'. To avoid using `ROLLBACK', you can use the following strategy: 1. Use `LOCK TABLES ...' to lock all the tables you want to access. 2. Test conditions. 3. Update if everything is okay. 4. Use `UNLOCK TABLES' to release your locks. This is usually a much faster method than using transactions with possible `ROLLBACK's, although not always. The only situation this solution doesn't handle is when someone kills the threads in the middle of an update. In this case, all locks will be released but some of the updates may not have been executed. You can also use functions to update records in a single operation. You can get a very efficient application by using the following techniques: * Modify fields relative to their current value * Update only those fields that actually have changed For example, when we are doing updates to some customer information, we update only the customer data that have changed and test only that none of the changed data, or data that depend on the changed data, have changed compared to the original row. The test for changed data is done with the `WHERE' clause in the `UPDATE' statement. If the record wasn't updated, we give the client a message: "Some of the data you have changed have been changed by another user". Then we show the old row versus the new row in a window, so the user can decide which version of the customer record he should use. This gives us something that is similar to "column locking" but is actually even better, because we only update some of the columns, using values that are relative to their current values. This means that typical `UPDATE' statements look something like these: UPDATE tablename SET pay_back=pay_back+'relative change'; UPDATE customer SET customer_date='current_date', address='new address', phone='new phone', money_he_owes_us=money_he_owes_us+'new_money' WHERE customer_id=id AND address='old address' AND phone='old phone'; As you can see, this is very efficient and works even if another client has changed the values in the `pay_back' or `money_he_owes_us' columns. In many cases, users have wanted `ROLLBACK' and/or `LOCK TABLES' for the purpose of managing unique identifiers for some tables. This can be handled much more efficiently by using an `AUTO_INCREMENT' column and either the SQL function `LAST_INSERT_ID()' or the C API function `mysql_insert_id()'. *Note `mysql_insert_id()': mysql_insert_id. At TcX, we have never had any need for row-level locking because we have always been able to code around it. Some cases really need row locking, but they are very few. If you want row-level locking, you can use a flag column in the table and do something like this: UPDATE tbl_name SET row_flag=1 WHERE id=ID; *MySQL* returns 1 for the number of affected rows if the row was found and `row_flag' wasn't already 1 in the original row. You can think of it as *MySQL* changed the above query to: UPDATE tbl_name SET row_flag=1 WHERE id=ID and row_flag <> 1; The MySQL access privilege system ********************************* *MySQL* has an advanced but non-standard security/privilege system. This section describes how it works. What the privilege system does ============================== The primary function of the *MySQL* privilege system is to authenticate a user connecting from a given host, and to associate that user with *select*, *insert*, *update* and *delete* privileges on a database. Additional functionality includes the ability to have an anonymous user and to grant privileges for *MySQL*-specific functions such as `LOAD DATA INFILE' and administrative operations. MySQL user names and passwords ============================== There are several distinctions between the way user names and passwords are used by *MySQL*, and the way they are used by Unix or Windows: * User names, as used by *MySQL* for authentication purposes, have nothing to do with Unix user names (login names) or Windows user names. Most *MySQL* clients by default try to log in using the current Unix user name as the *MySQL* user name, but that is for convenience only. Client programs allow a different name to be specified with the `-u' or `--user' options. This means that you can't make a database secure in any way unless all *MySQL* user names have passwords. Anyone may attempt to connect to the server using any name, and they will succeed if they specify any name that doesn't have a password. * *MySQL* user names can be up to 16 characters long; Unix user names typically are limited to 8 characters. * *MySQL* passwords have nothing to do with Unix passwords. There is no necessary connection between the password you use to log in to a Unix machine and the password you use to access a database on that machine. * *MySQL* encrypts passwords using a different algorithm than the one used during the Unix login process. See the descriptions of the `PASSWORD()' and `ENCRYPT()' functions in *Note Miscellaneous functions::. Connecting to the MySQL server ============================== *MySQL* client programs generally require that you specify connection parameters when you want to access a *MySQL* server: the host you want to connect to, your user name and your password. For example, the `mysql' client can be started like this (optional arguments are enclosed between `[' and `]'): shell> mysql [-h host_name] [-u user_name] [-pyour_pass] Alternate forms of the `-h', `-u' and `-p' options are `--host=host_name', `--user=user_name' and `--password=your_pass'. Note that there is *no space* between `-p' or `--password=' and the password following it. *Note:* Specifing a password on the command line is not secure! Any user on your system may then find out your password by typing a command like: `ps auxww'. *Note Option files::. `mysql' uses default values for connection parameters that are missing from the command line: * The default hostname is `localhost'. * The default user name is your Unix login name. * No password is supplied if `-p' is missing. Thus, for a Unix user `joe', the following commands are equivalent: shell> mysql -h localhost -u joe shell> mysql -h localhost shell> mysql -u joe shell> mysql Other *MySQL* clients behave similarly. On Unix systems, you can specify different default values to be used when you make a connection, so that you need not enter them on the command line each time you invoke a client program. This can be done in a couple of ways: * You can specify connection parameters in the `[client]' section of the `.my.cnf' configuration file in your home directory. The relevant section of the file might look like this: [client] host=host_name user=user_name password=your_pass *Note Option files::. * You can specify connection parameters using environment values. The host can be specified using `MYSQL_HOST'. The *MySQL* user name can be specified using `USER' (this is for Windows only). The password can be specified using `MYSQL_PWD' (but this is insecure; see next section). If connection parameters are specified in multiple ways, values specified on the command line take precedence over values specified in configuration files and environment variables, and values in configuration files take precedence over values in environment variables. Keeping your password secure ============================ It is inadvisable to specify your password in a way that exposes it to discovery by other users. The methods you can use to specify your password when you run client programs are listed below, along with an assessment of the risks of each method: * Use a `-pyour_pass' or `--password=your_pass' option on the command line. This is convenient but insecure, since your password becomes visible to system status programs (such as `ps') that may be invoked by other users to display command lines. (*MySQL* clients typically overwrite the command line argument with zeroes during their initialization sequence, but there is still a brief interval during which the value is visible.) * Use a `-p' or `--password' option (with no `your_pass' value specified). In this case, the client program solicits the password from the terminal: shell> mysql -u user_name -p Enter password: ******** The client echoes `*' characters to the terminal as you enter your password so that onlookers cannot see it. It is more secure to enter your password this way than to specify it on the command line because it is not visible to other users. However, this method of entering a password is suitable only for programs that you run interactively. If you want to invoke a client from a script that runs non-interactively, there is no opportunity to enter the password from the terminal. * Store your password in a configuration file. For example, you can list your password in the `[client]' section of the `.my.cnf' file in your home directory: [client] password=your_pass If you store your password in `.my.cnf', the file should not be group or world readable or writable. Make sure the file's access mode is `400' or `600'. *Note Option files::. * You can store your password in the `MYSQL_PWD' environment variable, but this method must be considered extremely insecure and should not be used. Some versions of `ps' include an option to display the environment of running processes; your password will be in plain sight for all to see if you set `MYSQL_PWD'. Even on systems without such a version of `ps', it is unwise to assume there is no other method to observe process environments. All in all, the safest methods are to have the client program prompt for the password or to specify the password in a properly-protected `.my.cnf' file. Privileges provided by MySQL ============================ Privilege information is stored in the `user', `db', `host', `tables_priv' and `columns_priv' tables in the `mysql' database (that is, in the database named `mysql'). The *MySQL* server reads the contents of these tables when it starts up and under the circumstances indicated in *Note Privilege changes::. The names used in this manual to refer to the privileges provided by *MySQL* are shown below, along with the table column name associated with each privilege in the grant tables and the context in which the privilege applies: *Privilege* *Column* *Context* *select* `Select_priv' tables *insert* `Insert_priv' tables *update* `Update_priv' tables *delete* `Delete_priv' tables *index* `Index_priv' tables *alter* `Alter_priv' tables *create* `Create_priv' databases, tables or indexes *drop* `Drop_priv' databases or tables *grant* `Grant_priv' databases or tables *references*`References_priv' databases or tables *reload* `Reload_priv' server administration *shutdown* `Shutdown_priv' server administration *process* `Process_priv' server administration *file* `File_priv' file access on server The *select*, *insert*, *update* and *delete* privileges allow you to perform operations on rows in existing tables in a database. `SELECT' statements require the *select* privilege only if they actually retrieve rows from a table. You can execute certain `SELECT' statements even without permission to access any of the databases on the server. For example, you could use the `mysql' client as a simple calculator: mysql> SELECT 1+1; mysql> SELECT PI()*2; The *index* privilege allows you to create or drop (remove) indexes. The *alter* privilege allows you to use `ALTER TABLE'. The *create* and *drop* privileges allow you to create new databases and tables, or to drop (remove) existing databases and tables. Note that if you grant the *drop* privilege for the `mysql' database to a user, that user can drop the database in which the *MySQL* access privileges are stored! The *grant* privilege allows you to give to other users those privileges you yourself possess. The *file* privilege gives you permission to read and write files on the server using the `LOAD DATA INFILE' and `SELECT ... INTO OUTFILE' statements. Any user to whom this privilege is granted can read or write any file that the *MySQL* server can read or write. The remaining privileges are used for administrative operations, which are performed using the `mysqladmin' program. The table below shows which `mysqladmin' commands each administrative privilege allows you to execute: *Privilege* *Commands permitted to privilege holders* *reload* `reload', `refresh', `flush-privileges', `flush-hosts', `flush-logs', `flush-tables' *shutdown* `shutdown' *process* `processlist', `kill' The `reload' command tells the server to reread the grant tables. The `refresh' command flushes all tables and opens and closes the log files. `flush-privileges' is a synonym for `reload'. The other `flush-*' commands perform functions similar to `refresh' but are more limited in scope, and may be preferable in some instances. For example, if you want to flush just the log files, `flush-logs' is a better choice than `refresh'. The `shutdown' command shuts down the server. The `processlist' command displays information about the threads executing within the server. The `kill' command kills server threads. You can always display or kill your own threads, but you need the *process* privilege to display or kill threads initiated by other users. It is a good idea in general to grant privileges only to those users who need them, but you should exercise particular caution in granting certain privileges: * The *grant* privilege allows users to give away their privileges to other users. Two users with different privileges and with the *grant* privilege are able to combine privileges. * The *alter* privilege may be used to subvert the privilege system by renaming tables. * The *file* privilege can be abused to read any world-readable file on the server into a database table, the contents of which can then be accessed using `SELECT'. * The *shutdown* privilege can be abused to deny service to other users entirely, by terminating the server. * The *process* privilege can be used to view the plain text of currently executing queries, including queries that set or change passwords. * Privileges on the `mysql' database can be used to change passwords and other access privilege information. (Passwords are stored encrypted, so a malicious user cannot simply read them. However, with sufficient privileges, that same user can replace a password with a different one.) There are some things that you cannot do with the *MySQL* privilege system: * You cannot explicitly specify that a given user should be denied access. That is, you cannot explicitly match a user and then refuse the connection. * You cannot specify that a user has privileges to create or drop tables in a database but not to create or drop the database itself. How the privilege system works ============================== The *MySQL* privilege system ensures that all users may do exactly the things that they are supposed to be allowed to do. When you connect to a *MySQL* server, your identity is determined by *the host from which you connect* and *the user name you specify*. The system grants privileges according to your identity and *what you want to do*. *MySQL* considers both your hostname and user name in identifying you because there is little reason to assume that a given user name belongs to the same person everywhere on the Internet. For example, the user `bill' who connects from `whitehouse.gov' need not be the same person as the user `bill' who connects from `mosoft.com'. *MySQL* handles this by allowing you to distinguish users on different hosts that happen to have the same name: you can grant `bill' one set of privileges for connections from `whitehouse.gov', and a different set of privileges for connections from `microsoft.com'. *MySQL* access control involves two stages: * Stage 1: The server checks whether or not you are even allowed to connect. * Stage 2: Assuming you can connect, the server checks each request you issue to see whether or not you have sufficient privileges to perform it. For example, if you try to select rows from a table in a database or drop a table from the database, the server makes sure you have the *select* privilege for the table or the *drop* privilege for the database. The server uses the `user', `db' and `host' tables in the `mysql' database at both stages of access control. The fields in these grant tables are shown below: *Table name* `user' `db' `host' *Scope `Host' `Host' `Host' fields* `User' `Db' `Db' `Password' `User' *Privilege `Select_priv' `Select_priv' `Select_priv' fields* `Insert_priv' `Insert_priv' `Insert_priv' `Update_priv' `Update_priv' `Update_priv' `Delete_priv' `Delete_priv' `Delete_priv' `Index_priv' `Index_priv' `Index_priv' `Alter_priv' `Alter_priv' `Alter_priv' `Create_priv' `Create_priv' `Create_priv' `Drop_priv' `Drop_priv' `Drop_priv' `Grant_priv' `Grant_priv' `Grant_priv' `Reload_priv' `Shutdown_priv' `Process_priv' `File_priv' For the second stage of access control (request verification), the server may, if the request involves tables, additionally consult the `tables_priv' and `columns_priv' tables. The fields in these tables are shown below: *Table name* `tables_priv' `columns_priv' *Scope `Host' `Host' fields* `Db' `Db' `User' `User' `Table_name' `Table_name' `Column_name' *Privilege `Table_priv' `Column_priv' fields* `Column_priv' *Other `Timestamp' `Timestamp' fields* `Grantor' Each grant table contains scope fields and privilege fields. Scope fields determine the scope of each entry in the tables, i.e., the context in which the entry applies. For example, a `user' table entry with `Host' and `User' values of `'thomas.loc.gov'' and `'bob'' would be used for authenticating connections made to the server by `bob' from the host `thomas.loc.gov'. Similarly, a `db' table entry with `Host', `User' and `Db' fields of `'thomas.loc.gov'', `'bob'' and `'reports'' would be used when `bob' connects from the host `thomas.loc.gov' to access the `reports' database. The `tables_priv' and `columns_priv' tables contain scope fields indicating tables or table/column combinations to which each entry applies. For access-checking purposes, comparisons of `Host' values are case insensitive. `User', `Password', `Db' and `Table_name' values are case sensitive. `Column_name' values are case insensitive in *MySQL* 3.22.12 or later. Privilege fields indicate the privileges granted by a table entry, that is, what operations can be performed. The server combines the information in the various grant tables to form a complete description of a user's privileges. The rules used to do this are described in *Note Request access::. Scope fields are strings, declared as shown below; the default value for each is the empty string: *Field *Type* name* `Host' `CHAR(60)' `User' `CHAR(16)' `Password' `CHAR(16)' `Db' `CHAR(64)' (`CHAR(60)' for the `tables_priv' and `columns_priv' tables) In the `user', `db' and `host' tables, all privilege fields are declared as `ENUM('N','Y')' -- each can have a value of `'N'' or `'Y'', and the default value is `'N''. In the `tables_priv' and `columns_priv' tables, the privilege fields are declared as `SET' fields: *Table name* *Field name* *Possible set elements* `tables_priv' `Table_priv' `'Select', 'Insert', 'Update', 'Delete', 'Create', 'Drop', 'Grant', 'References', 'Index', 'Alter'' `tables_priv' `Column_priv' `'Select', 'Insert', 'Update', 'References'' `columns_priv' `Column_priv' `'Select', 'Insert', 'Update', 'References'' Briefly, the server uses the grant tables like this: * The `user' table scope fields determine whether to allow or reject incoming connections. For allowed connections, the privilege fields indicate the user's global (superuser) privileges. * The `db' and `host' tables are used together: - The `db' table scope fields determine which users can access which databases from which hosts. The privilege fields determine which operations are allowed. - The `host' table is used as an extension of the `db' table when you want a given `db' table entry to apply to several hosts. For example, if you want a user to be able to use a database from several hosts in your network, leave the `Host' value empty in the user's `db' table entry, then populate the `host' table with an entry for each of those hosts. This mechanism is described more detail in *Note Request access::. * The `tables_priv' and `columns_priv' tables are similar to the `db' table, but are more fine-grained: they apply at the table and column level rather than at the database level. Note that administrative privileges (*reload*, *shutdown*, etc.) are specified only in the `user' table. This is because administrative operations are operations on the server itself and are not database-specific, so there is no reason to list such privileges in the other grant tables. In fact, only the `user' table need be consulted to determine whether or not you can perform an administrative operation. The *file* privilege is specified only in the `user' table, too. It is not an administrative privilege as such, but your ability to read or write files on the server host is independent of the database you are accessing. The `mysqld' server reads the contents of the grant tables once, when it starts up. Changes to the grant tables take effect as indicated in *Note Privilege changes::. When you modify the contents of the grant tables, it is a good idea to make sure that your changes set up privileges the way you want. For help in diagnosing problems, see *Note Access denied::. For advice on security issues, *Note Security::. A useful diagnostic tool is the `mysqlaccess' script, which Yves Carlier has provided for the *MySQL* distribution. Invoke `mysqlaccess' with the `--help' option to find out how it works. Note that `mysqlaccess' checks access using only the `user', `db' and `host' tables. It does not check table- or column-level privileges. Access control, stage 1: Connection verification ================================================ When you attempt to connect to a *MySQL* server, the server accepts or rejects the connection based on your identity and whether or not you can verify your identity by supplying the correct password. If not, the server denies access to you completely. Otherwise, the server accepts the connection, then enters stage 2 and waits for requests. Your identity is based on two pieces of information: * The host from which you connect * Your *MySQL* user name Identity checking is performed using the three `user' table scope fields (`Host', `User' and `Password'). The server accepts the connection only if a `user' table entry matches your hostname and user name, and you supply the correct password. Values in the `user' table scope fields may be specified as follows: * A `Host' value may be a hostname or an IP number, or `'localhost'' to indicate the local host. * You can use the wildcard characters `%' and `_' in the `Host' field. * A `Host' value of `'%'' matches any hostname. A blank `Host' value is equivalent to `'%''. Note that these values match *any host that can create a connection to your server!* * Wildcard characters are not allowed in the `User' field, but you can specify a blank value, which matches any name. If the `user' table entry that matches an incoming connection has a blank user name, the user is considered to be the anonymous user (the user with no name), rather than the name that the client actually specified. This means that a blank user name is used for all further access checking for the duration of the connection (that is, during stage 2). * The `Password' field can be blank. This does not mean that any password matches, it means the user must connect without specifying a password. Non-blank `Password' values represent encrypted passwords. *MySQL* does not store passwords in plaintext form for anyone to see. Rather, the password supplied by a user who is attempting to connect is encrypted (using the `PASSWORD()' function) and compared to the already-encrypted version stored in the `user' table. If they match, the password is correct. The examples below show how various combinations of `Host' and `User' values in `user' table entries apply to incoming connections: `Host' *value* `User' *Connections matched by entry* *value* `'thomas.loc.gov'' `'fred'' `fred', connecting from `thomas.loc.gov' `'thomas.loc.gov'' `''' Any user, connecting from `thomas.loc.gov' `'%'' `'fred'' `fred', connecting from any host `'%'' `''' Any user, connecting from any host `'%.loc.gov'' `'fred'' `fred', connecting from any host in the `loc.gov' domain `'x.y.%'' `'fred'' `fred', connecting from `x.y.net', `x.y.com',`x.y.edu', etc. (this is probably not useful) `'144.155.166.177''`'fred'' `fred', connecting from the host with IP address `144.155.166.177' `'144.155.166.%'' `'fred'' `fred', connecting from any host in the `144.155.166' class C subnet Since you can use IP wildcard values in the `Host' field (e.g., `'144.155.166.%'' to match every host on a subnet), there is the possibility that someone might try to exploit this capability by naming a host `144.155.166.somewhere.com'. To foil such attempts, *MySQL* disallows matching on hostnames that start with digits and a dot. Thus, if you have a host named something like `1.2.foo.com', its name will never match the `Host' column of the grant tables. Only an IP number can match an IP wildcard value. An incoming connection may be matched by more than one entry in the `user' table. For example, a connection from `thomas.loc.gov' by `fred' would be matched by several of the entries just shown above. How does the server choose which entry to use if more than one matches? The server resolves this question by sorting the `user' table after reading it at startup time, then looking through the entries in sorted order when a user attempts to connect. The first matching entry is the one that is used. `user' table sorting works as follows. Suppose the `user' table looks like this: +-----------+----------+- | Host | User | ... +-----------+----------+- | % | root | ... | % | jeffrey | ... | localhost | root | ... | localhost | | ... +-----------+----------+- When the server reads in the table, it orders the entries with the most-specific `Host' values first (`'%'' in the `Host' column means "any host" and is least specific). Entries with the same `Host' value are ordered with the most-specific `User' values first (a blank `User' value means "any user" and is least specific). The resulting sorted `user' table looks like this: +-----------+----------+- | Host | User | ... +-----------+----------+- | localhost | root | ... | localhost | | ... | % | jeffrey | ... | % | root | ... +-----------+----------+- When a connection is attempted, the server looks through the sorted entries and uses the first match found. For a connection from `localhost' by `jeffrey', the entries with `'localhost'' in the `Host' column match first. Of those, the entry with the blank user name matches both the connecting hostname and user name. (The `'%'/'jeffrey'' entry would have matched, too, but it is not the first match in the table.) Here is another example. Suppose the `user' table looks like this: +----------------+----------+- | Host | User | ... +----------------+----------+- | % | jeffrey | ... | thomas.loc.gov | | ... +----------------+----------+- The sorted table looks like this: +----------------+----------+- | Host | User | ... +----------------+----------+- | thomas.loc.gov | | ... | % | jeffrey | ... +----------------+----------+- A connection from `thomas.loc.gov' by `jeffrey' is matched by the first entry, whereas a connection from `whitehouse.gov' by `jeffrey' is matched by the second. A common misconception is to think that for a given user name, all entries that explicitly name that user will be used first when the server attempts to find a match for the connection. This is simply not true. The previous example illustrates this, where a connection from `thomas.loc.gov' by `jeffrey' is first matched not by the entry containing `'jeffrey'' as the `User' field value, but by the entry with no user name! If you have problems connecting to the server, print out the `user' table and sort it by hand to see where the first match is being made. Access control, stage 2: Request verification ============================================= Once you establish a connection, the server enters stage 2. For each request that comes in on the connection, the server checks whether you have sufficient privileges to perform it, based on the type of operation you wish to perform. This is where the privilege fields in the grant tables come into play. These privileges can come from any of the `user', `db', `host', `tables_priv' or `columns_priv' tables. The grant tables are manipulated with `GRANT' and `REVOKE' commands. *Note `GRANT': GRANT. (You may find it helpful to refer to *Note Privileges::, which lists the fields present in each of the grant tables.) The `user' table grants privileges that are assigned to you on a global basis and that apply no matter what the current database is. For example, if the `user' table grants you the *delete* privilege, you can delete rows from any database on the server host! In other words, `user' table privileges are superuser privileges. It is wise to grant privileges in the `user' table only to superusers such as server or database administrators. For other users, you should leave the privileges in the `user' table set to `'N'' and grant privileges on a database-specific basis only, using the `db' and `host' tables. The `db' and `host' tables grant database-specific privileges. Values in the scope fields may be specified as follows: * The wildcard characters `%' and `_' can be used in the `Host' and `Db' fields of either table. * A `'%'' `Host' value in the `db' table means "any host." A blank `Host' value in the `db' table means "consult the `host' table for further information." * A `'%'' or blank `Host' value in the `host' table means "any host." * A `'%'' or blank `Db' value in either table means "any database." * A blank `User' value in either table matches the anonymous user. The `db' and `host' tables are read in and sorted when the server starts up (at the same time that it reads the `user' table). The `db' table is sorted on the `Host', `Db' and `User' scope fields, and the `host' table is sorted on the `Host' and `Db' scope fields. As with the `user' table, sorting puts the most-specific values first and least-specific values last, and when the server looks for matching entries, it uses the first match that it finds. The `tables_priv' and `columns_priv' tables grant table- and column-specific privileges. Values in the scope fields may be specified as follows: * The wildcard characters `%' and `_' can be used in the `Host' field of either table. * A `'%'' or blank `Host' value in either table means "any host." * The `Db', `Table_name' and `Column_name' fields cannot contain wildcards or be blank in either table. The `tables_priv' and `columns_priv' tables are sorted on the `Host', `Db' and `User' fields. This is similar to `db' table sorting, although since only the `Host' field may contain wildcards, the sorting is simpler. The request verification process is described below. (If you are familiar with the access-checking source code, you will notice that the description here differs slightly from the algorithm used in the code. The description is equivalent to what the code actually does; it differs only to make the explanation simpler.) For administrative requests (*shutdown*, *reload*, etc.), the server checks only the `user' table entry, since that is the only table that specifies administrative privileges. Access is granted if the entry allows the requested operation and denied otherwise. For example, if you want to execute `mysqladmin shutdown' but your `user' table entry doesn't grant the *shutdown* privilege to you, access is denied without even checking the `db' or `host' tables. (Since they contain no `Shutdown_priv' column, there is no need to do so.) For database-related requests (*insert*, *update*, etc.), the server first checks the user's global (superuser) privileges by looking in the `user' table entry. If the entry allows the requested operation, access is granted. If the global privileges in the `user' table are insufficient, the server determines the user's database-specific privileges by checking the `db' and `host' tables: 1. The server looks in the `db' table for a match on the `Host', `Db' and `User' fields. `Host' and `User' are matched to the connecting user's hostname and *MySQL* user name. The `Db' field is matched to the database the user wants to access. If there is no entry for the `Host' and `User', access is denied. 2. If there is a matching `db' table entry and its `Host' field is not blank, that entry defines the user's database-specific privileges. 3. If the matching `db' table entry's `Host' field is blank, it signifies that the `host' table enumerates which hosts should be allowed access to the database. In this case, a further lookup is done in the `host' table to find a match on the `Host' and `Db' fields. If no `host' table entry matches, access is denied. If there is a match, the user's database-specific privileges are computed as the intersection (*not* the union!) of the privileges in the `db' and `host' table entries, i.e., the privileges that are `'Y'' in both entries. (This way you can grant general privileges in the `db' table entry and then selectively restrict them on a host-by-host basis using the `host' table entries.) After determining the database-specific privileges granted by the `db' and `host' table entries, the server adds them to the global privileges granted by the `user' table. If the result allows the requested operation, access is granted. Otherwise, the server checks the user's table and column privileges in the `tables_priv' and `columns_priv' tables and adds those to the user's privileges. Access is allowed or denied based on the result. Expressed in boolean terms, the preceding description of how a user's privileges are calculated may be summarized like this: global privileges OR (database privileges AND host privileges) OR table privileges OR column privileges It may not be apparent why, if the global `user' entry privileges are initially found to be insufficient for the requested operation, the server adds those privileges to the database-, table- and column-specific privileges later. The reason is that a request might require more than one type of privilege. For example, if you execute an `INSERT ... SELECT' statement, you need both *insert* and *select* privileges. Your privileges might be such that the `user' table entry grants one privilege and the `db' table entry grants the other. In this case, you have the necessary privileges to perform the request, but the server cannot tell that from either table by itself; the privileges granted by both entries must be combined. The `host' table can be used to maintain a list of "secure" servers. At TcX, the `host' table contains a list of all machines on the local network. These are granted all privileges. You can also use the `host' table to indicate hosts that are *not* secure. Suppose you have a machine `public.your.domain' that is located in a public area that you do not consider secure. You can allow access to all hosts on your network except that machine by using `host' table entries like this: +--------------------+----+- | Host | Db | ... +--------------------+----+- | public.your.domain | % | ... (all privileges set to 'N') | %.your.domain | % | ... (all privileges set to 'Y') +--------------------+----+- Naturally, you should always test your entries in the grant tables (e.g., using `mysqlaccess') to make sure your access privileges are actually set up the way you think they are. When privilege changes take effect ================================== When `mysqld' starts, all grant table contents are read into memory and become effective at that point. Modifications to the grant tables that you perform using `GRANT', `REVOKE', or `SET PASSWORD' are noticed by the server immediately. If you modify the grant tables manually (using `INSERT', `UPDATE', etc.), you should execute a `FLUSH PRIVILEGES' statement or run `mysqladmin flush-privileges' to tell the server to reload the grant tables. Otherwise your changes will have *no effect* until you restart the server. When the server notices that the grant tables have been changed, existing client connections are affected as follows: * Table and column privilege changes take effect with the client's next request. * Database privilege changes take effect at the next `USE db_name' command. Global privilege changes and password changes take effect the next time the client connects. Setting up the initial MySQL privileges ======================================= After installing *MySQL*, you set up the initial access privileges by running `scripts/mysql_install_db'. *Note Quick install::. The `scripts/mysql_install_db' script starts up the `mysqld' server, then initializes the grant tables to contain the following set of privileges: * The *MySQL* `root' user is created as a superuser who can do anything. Connections must be made from the local host. *Note:* The initial `root' password is empty, so anyone can connect as `root' *without a password* and be granted all privileges. * An anonymous user is created that can do anything with databases that have a name of `'test'' or starting with `'test_''. Connections must be made from the local host. This means any local user can connect and be treated as the anonymous user. * Other privileges are denied. For example, normal users can't use `mysqladmin shutdown' or `mysqladmin processlist'. *Note:* The default privileges are different for Win32. *Note Win32 running::. Since your installation is initially wide open, one of the first things you should do is specify a password for the *MySQL* `root' user. You can do this as follows (note that you specify the password using the `PASSWORD()' function): shell> mysql -u root mysql mysql> UPDATE user SET Password=PASSWORD('new_password') WHERE user='root'; mysql> FLUSH PRIVILEGES; You can also use the `SET PASSWORD' statement: shell> mysql -u root mysql mysql> SET PASSWORD FOR root=PASSWORD('new_password'); Another way to set the password is by using the `mysqladmin' command: shell> mysqladmin -u root password new_password Note that if you update the password in the `user' table directly using the first method, you must tell the server to reread the grant tables (with `FLUSH PRIVILEGES'), since the change will go unnoticed otherwise. Once the `root' password has been set, thereafter you must supply that password when you connect to the server as `root'. You may wish to leave the `root' password blank so that you don't need to specify it while you perform additional setup or testing, but be sure to set it before using your installation for any real production work. See the `scripts/mysql_install_db' script to see how it sets up the default privileges. You can use this as a basis to see how to add other users. If you want the initial privileges to be different than those just described above, you can modify `mysql_install_db' before you run it. To recreate the grant tables completely, remove all the `*.frm', `*.ISM' and `*.ISD' files in the directory containing the `mysql' database. (This is the directory named `mysql' under the database directory, which is listed when you run `mysqld --help'.) Then run the `mysql_install_db' script, possibly after editing it first to have the privileges you want. *NOTE:* For *MySQL* versions older than 3.22.10, you should NOT delete the `*.frm' files. If you accidentally do this, you should copy them back from your *MySQL* distribution before running `mysql_install_db'. Adding new user privileges to MySQL =================================== You can add users two different ways: by using `GRANT' statements or by manipulating the *MySQL* grant tables directly. The preferred method is to use `GRANT' statements, because they are more concise and less error-prone. The examples below show how to use the `mysql' client to set up new users. These examples assume that privileges are set up according to the defaults described in the previous section. This means that to make changes, you must be on the same machine where `mysqld' is running, you must connect as the *MySQL* `root' user, and the `root' user must have the *insert* privilege for the `mysql' database and the *reload* administrative privilege. Also, if you have changed the `root' user password, you must specify it for the `mysql' commands below. You can add new users by issuing `GRANT' statements: shell> mysql --user=root mysql mysql> GRANT ALL PRIVILEGES ON *.* TO monty@localhost IDENTIFIED BY 'something' WITH GRANT OPTION; mysql> GRANT ALL PRIVILEGES ON *.* TO monty@"%" IDENTIFIED BY 'something' WITH GRANT OPTION; mysql> GRANT RELOAD,PROCESS ON *.* TO admin@localhost; mysql> GRANT USAGE ON *.* TO dummy@localhost; These `GRANT' statements set up three new users: `monty' A full superuser who can connect to the server from anywhere, but who must use a password (`'something'' to do so. Note that we must issue `GRANT' statements for both `monty@localhost' and `monty@"%"'. If we don't add the entry with `localhost', the anonymous user entry for `localhost' that is created by `mysql_install_db' will take precedence when we connect from the local host, because it has a more specific `Host' field value and thuse comes earlier in the `user' table sort order. `admin' A user who can connect from `localhost' without a password and who is granted the *reload* and *process* administrative privileges. This allows the user to execute the `mysqladmin reload', `mysqladmin refresh' and `mysqladmin flush-*' commands, as well as `mysqladmin processlist' . No database-related privileges are granted. They can be granted later by issuing additional `GRANT' statements. `dummy' A user who can connect without a password, but only from the local host. The global privileges are all set to `'N'' -- the `USAGE' privilege type allows you to set up a user with no privileges. It is assumed that you will grant database-specific privileges later. You can also add the same user access information directly by issuing `INSERT' statements and then telling the server to reload the grant tables: shell> mysql --user=root mysql mysql> INSERT INTO user VALUES('localhost','monty',PASSWORD('something'), 'Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y') mysql> INSERT INTO user VALUES('%','monty',PASSWORD('something'), 'Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y') mysql> INSERT INTO user SET Host='localhost',User='admin', Reload_priv='Y', Process_priv='Y'; mysql> INSERT INTO user (Host,User,Password) VALUES('localhost','dummy',''); mysql> FLUSH PRIVILEGES; Depending on your *MySQL* version, you may have to use a different number of `'Y'' values above (versions prior to 3.22.11 had fewer privilege columns). For the `admin' user, the more readable extended `INSERT' syntax that is available starting with 3.22.11 is used. Note that to set up a superuser, you need only create a `user' table entry with the privilege fields set to `'Y''. No `db' or `host' table entries are necessary. The privilege columns in the `user' table were not set explicitly in the last `INSERT' statement (for the `dummy' user), so those columns are assigned the default value of `'N''. This is the same thing that `GRANT USAGE' does. The following example adds a user `custom' who can connect from hosts `localhost', `server.domain' and `whitehouse.gov'. He wants to access the `bankaccount' database only from `localhost', the `expenses' database only from `whitehouse.gov' and the `customer' database from all three hosts. He wants to use the password `stupid' from all three hosts. To set up this user's privileges using `GRANT' statements, run these commands: shell> mysql --user=root mysql mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP ON bankaccount.* TO custom@localhost IDENTIFIED BY 'stupid'; mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP ON expenses.* TO custom@whitehouse.gov IDENTIFIED BY 'stupid'; mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP ON customer.* TO custom@'%' IDENTIFIED BY 'stupid'; To set up the user's privileges by modifying the grant tables directly, run these commands (note the `FLUSH PRIVILEGES' at the end): shell> mysql --user=root mysql mysql> INSERT INTO user (Host,User,Password) VALUES('localhost','custom',PASSWORD('stupid')); mysql> INSERT INTO user (Host,User,Password) VALUES('server.domain','custom',PASSWORD('stupid')); mysql> INSERT INTO user (Host,User,Password) VALUES('whitehouse.gov','custom',PASSWORD('stupid')); mysql> INSERT INTO db (Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv, Create_priv,Drop_priv) VALUES ('localhost','bankaccount','custom','Y','Y','Y','Y','Y','Y'); mysql> INSERT INTO db (Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv, Create_priv,Drop_priv) VALUES ('whitehouse.gov','expenses','custom','Y','Y','Y','Y','Y','Y'); mysql> INSERT INTO db (Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv, Create_priv,Drop_priv) VALUES('%','customer','custom','Y','Y','Y','Y','Y','Y'); mysql> FLUSH PRIVILEGES; The first three `INSERT' statements add `user' table entries that allow user `custom' to connect from the various hosts with the given password, but grant no permissions to him (all privileges are set to the default value of `'N''). The next three `INSERT' statements add `db' table entries that grant privileges to `custom' for the `bankaccount', `expenses' and `customer' databases, but only when accessed from the proper hosts. As usual, when the grant tables are modified directly, the server must be told to reload them (with `FLUSH PRIVILEGES') so that the privilege changes take effect. If you want to give a specific user access from any machine in a given domain, you can issue a `GRANT' statement like the following: mysql> GRANT ... ON *.* TO myusername@"%.mydomainname.com" IDENTIFIED BY 'mypassword'; To do the same thing by modifying the grant tables directly, do this: mysql> INSERT INTO user VALUES ('%.mydomainname.com', 'myusername', PASSWORD('mypassword'),...); mysql> FLUSH PRIVILEGES; You can also use `xmysqladmin', `mysql_webadmin' and even `xmysql' to insert, change and update values in the grant tables. You can find these utilities at the *MySQL* Contrib directory (http://www.mysql.com/Contrib/). How to set up passwords ======================= The examples in the preceding sections illustrate an important principle: when you store a non-empty password using `INSERT' or `UPDATE' statements, you must use the `PASSWORD()' function to encrypt it. This is because the `user' table stores passwords in encrypted form, not as plaintext. If you forget that fact, you are likely to attempt to set passwords like this: shell> mysql -u root mysql mysql> INSERT INTO user (Host,User,Password) VALUES('%','jeffrey','biscuit'); mysql> FLUSH PRIVILEGES; The result is that the plaintext value `'biscuit'' is stored as the password in the `user' table. When the user `jeffrey' attempts to connect to the server using this password, the `mysql' client encrypts it with `PASSWORD()' and sends the result to the server. The server compares the value in the `user' table (which is the plaintext value `'biscuit'') to the encrypted password (which is *not* `'biscuit''). The comparison fails and the server rejects the connection: shell> mysql -u jeffrey -pbiscuit test Access denied Since passwords must be encrypted when they are inserted in the `user' table, the `INSERT' statement should have been specified like this instead: mysql> INSERT INTO user (Host,User,Password) VALUES('%','jeffrey',PASSWORD('biscuit')); You must also use the `PASSWORD()' function when you use `SET PASSWORD' statements: mysql> SET PASSWORD FOR jeffrey@"%" = PASSWORD('biscuit'); If you set passwords using the `GRANT ... IDENTIFIED BY' statement or the `mysqladmin password' command, the `PASSWORD()' function is unnecessary. They both take care of encrypting the password for you, so you would specify a password of `'biscuit'' like this: mysql> GRANT USAGE ON *.* TO jeffrey@"%" IDENTIFIED BY 'biscuit'; or shell> mysqladmin -u jeffrey password biscuit Note: `PASSWORD()' does not perform password encryption in the same way that Unix passwords are encrypted. You should not assume that if your Unix password and your *MySQL* password are the same, `PASSWORD()' will result in the same encrypted value as is stored in the Unix password file. *Note User names::. Causes of `Access denied' errors ================================ If you encounter `Access denied' errors when you try to connect to the *MySQL* server, the list below indicates some courses of action you can take to correct the problem: * Did you run the `mysql_install_db' script after installing *MySQL*, to set up the initial grant table contents? If not, do so. *Note Default privileges::. Test the initial privileges by executing this command: shell> mysql -u root test The server should let you connect without error. You should also make sure you have a file `user.ISD' in the *MySQL* database directory. Ordinarily, this is `PATH/var/mysql/user.ISD', where `PATH' is the pathname to the *MySQL* installation root. * After a fresh installation, you should connect to the server and set up your users and their access permissions: shell> mysql -u root mysql The server should let you connect because the *MySQL* `root' user has no password initially. Since that is also a security risk, setting the `root' password is something you should do while you're setting up your other *MySQL* users. If you try to connect as `root' and get this error: Access denied for user: '@unknown' to database mysql this means that you don't have an entry in the `user' table with a `User' column value of `'root'' and that `mysqld' cannot resolve the hostname for your client. In this case, you must restart the server with the `--skip-grant-tables' option and edit your `/etc/hosts' or `\windows\hosts' file to add a entry for your host. * If you updated an existing *MySQL* installation from a pre-3.22.11 version to 3.22.11 or later, did you run the `mysql_fix_privilege_tables' script? If not, do so. The structure of the grant tables changed with *MySQL* 3.22.11 when the `GRANT' statement became functional. * If you make changes to the grant tables directly (using `INSERT' or `UPDATE' statement) and your changes seem to be ignored, remember that you must issue a `FLUSH PRIVILEGES' statement or execute a `mysqladmin flush-privileges' command to cause the server to reread the tables. Otherwise your changes have no effect until the next time the server is restarted. Remember that after you set the `root' password, you won't need to specify it until after you flush the privileges, because the server still won't know you've changed the password yet! * If your privileges seem to have changed in the middle of a session, it may be that a superuser has changed them. Reloading the grant tables affects new client connections, but it also affects existing connections as indicated in *Note Privilege changes::. * For testing, start the `mysqld' daemon with the `--skip-grant-tables' option. Then you can change the *MySQL* grant tables and use the `mysqlaccess' script to check whether or not your modifications have the desired effect. When you are satisfied with your changes, execute `mysqladmin flush-privileges' to tell the `mysqld' server to start using the new grant tables. *Note:* Reloading the grant tables overrides the `--skip-grant-tables' option. This allows you to tell the server to begin using the grant tables again without bringing it down and restarting it. * If you have access problems with a Perl, Python or ODBC program, try to connect to the server with `mysql -u user_name db_name' or `mysql -u user_name -pyour_pass db_name'. If you are able to connect using the `mysql' client, there is a problem with your program and not with the access privileges. (Notice that there is no space between `-p' and the password; you can also use the `--password=your_pass' syntax to specify the password.) * If you can't get your password to work, remember that you must use the `PASSWORD()' function if you set the password with the `INSERT', `UPDATE' or `SET PASSWORD' statements. The `PASSWORD()' function is unnecessary if you specify the password using the `GRANT ... INDENTIFIED BY' statement or the `mysqladmin password' command. *Note Passwords::. * `localhost' is a synonym for your local hostname, and is also the default host to which clients try to connect if you specify no host explicitly. However, connections to `localhost' do not work if you are running on a system that uses MIT-pthreads (`localhost' connections are made using Unix sockets, which are not supported by MIT-pthreads). To avoid this problem on such systems, you should use the `--host' option to name the server host explicitly. This will make a TCP/IP connection to the `mysqld' server. In this case, you must have your real hostname in `user' table entries on the server host. (This is true even if you are running a client program on the same host as the server.) * If you get an `Access denied' error when trying to connect to the database with `mysql -u user_name db_name', you may have a problem with the `user' table. Check this by executing `mysql -u root mysql' and issuing this SQL statement: mysql> SELECT * FROM user; The result should include an entry with the `Host' and `User' columns matching your computer's hostname and your *MySQL* user name. * The `Access denied' error message will tell you who you are trying to log in as, the host from which you are trying to connect, and whether or not you were using a password. Normally, you should have one entry in the `user' table that exactly matches the hostname and user name that were given in the error message. * If you get the following error when you try to connect from a different host than the one on which the *MySQL* server is running, then there is no row in the `user' table that matches that host: Host ... is not allowed to connect to this MySQL server You can fix this by using the command line tool `mysql' (on the server host!) to add a row to the `user' table for the user/hostname combination from which you are trying to connect. If you are not running *MySQL* 3.22 and you don't know the IP number or hostname of the machine from which you are connecting, you should put an entry with `'%'' as the `Host' column value in the `user' table and restart `mysqld' with the `--log' option on the server machine. After trying to connect from the client machine, the information in the *MySQL* log will indicate how you really did connect. (Then replace the `'%'' in the `user' table entry with the actual hostname that shows up in the log. Otherwise, you'll have a system that is insecure.) * If `mysql -u root test' works but `mysql -h your_hostname -u root test' results in `Access denied', then you may not have the correct name for your host in the `user' table. A common problem here is that the `Host' value in the user table entry specifies an unqualified hostname, but your system's name resolution routines return a fully-qualified domain name (or vice-versa). For example, if you have an entry with host `'tcx'' in the `user' table, but your DNS tells *MySQL* that your hostname is `'tcx.subnet.se'', the entry will not work. Try adding an entry to the `user' table that contains the IP number of your host as the `Host' column value. (Alternatively, you could add an entry to the `user' table with a `Host' value that contains a wildcard--for example, `'tcx.%''. However, use of hostnames ending with `%' is *insecure* and is *not* recommended!) * If `mysql -u user_name test' works but `mysql -u user_name other_db_name' doesn't work, you don't have an entry for `other_db_name' listed in the `db' table. * If `mysql -u user_name db_name' works when executed on the server machine, but `mysql -u host_name -u user_name db_name' doesn't work when executed on another client machine, you don't have the client machine listed in the `user' table or the `db' table. * If you can't figure out why you get `Access denied', remove from the `user' table all entries that have `Host' values containing wildcards (entries that contain `%' or `_'). A very common error is to insert a new entry with `Host'=`'%'' and `User'=`'some user'', thinking that this will allow you to specify `localhost' to connect from the same machine. The reason that this doesn't work is that the default privileges include an entry with `Host'=`'localhost'' and `User'=`'''. Since that entry has a `Host' value `'localhost'' that is more specific than `'%'', it is used in preference to the new entry when connecting from `localhost'! The correct procedure is to insert a second entry with `Host'=`'localhost'' and `User'=`'some_user'', or to remove the entry with with `Host'=`'localhost'' and `User'=`'''. * If you get the following error, you may have a problem with the `db' or `host' table: Access to database denied If the entry selected from the `db' table has an empty value in the `Host' column, make sure there are one or more corresponding entries in the `host' table specifying which hosts the `db' table entry applies to. If you get the error when using the SQL commands `SELECT ... INTO OUTFILE' or `LOAD DATA INFILE', your entry in the `user' table probably doesn't have the *file* privilege enabled. * Remember that client programs will use connection parameters specified in configuration files or environment variables. If a client seems to be sending the wrong default connection parameters when you don't specify them on the command line, check your environment and the `.my.cnf' file in your home directory. You might also check the system-wide *MySQL* configuration files, though it is far less likely that client connection parameters will be specified there. *Note Option files::. If you get `Access denied' when you run a client without any options, make sure you haven't specified an old password in any of your option files! *Note Option files::. * If everything else fails, start the `mysqld' daemon with a debugging option (for example, `--debug=d,general,query'). This will print host and user information about attempted connections, as well as information about each command issued. *Note Debugging server::. * If you have any other problems with the *MySQL* grant tables and feel you must post the problem to the mailing list, always provide a dump of the *MySQL* grant tables. You can dump the tables with the `mysqldump mysql' command. As always, post your problem using the `mysqlbug' script. In some cases you may restart `mysqld' with `--skip-grant-tables' to be able to run `mysqldump'. How to make MySQL secure against crackers ========================================= When you connect to a *MySQL* server, you should normally use a password. The password is not transmitted in clear text over the connection. All other information is transferred as text that can be read by anyone that is able to watch the connection. If you are concerned about this, you can use the compressed protocol (in *MySQL* 3.22 and above) to make things much harder. To make things even more secure you should install `ssh' (see `http://www.cs.hut.fi/ssh'). With this, you can get an encrypted TCP/IP connection between a *MySQL* server and a *MySQL* client. To make a *MySQL* system secure, you should strongly consider the following suggestions: * Use passwords for all *MySQL* users. Remember that anyone can log in as any other person as simply as `mysql -u other_user db_name' if `other_user' has no password. It is common behavior with client/server applications that the client may specify any user name. You can change the password of all users by editing the `mysql_install_db' script before you run it, or only the password for the *MySQL* `root' user like this: shell> mysql -u root mysql mysql> UPDATE user SET Password=PASSWORD('new_password') WHERE user='root'; mysql> FLUSH PRIVILEGES; * Don't run the *MySQL* daemon as the Unix `root' user. `mysqld' can be run as any user. You can also create a new Unix user `mysql' to make everything even more secure. If you run `mysqld' as another Unix user, you don't need to change the `root' user name in the `user' table, because *MySQL* user names have nothing to do with Unix user names. You can edit the `mysql.server' script to start `mysqld' as another Unix user. Normally this is done with the `su' command. For more details, see *Note Changing *MySQL* user: Changing MySQL user. * If you put a password for the Unix `root' user in the `mysql.server' script, make sure this script is readable only by `root'. * Check that the Unix user that `mysqld' runs as is the only user with read/write privileges in the database directories. * Don't give the *process* privilege to all users. The output of `mysqladmin processlist' shows the text of the currently executing queries, so any user who is allowed to execute that command might be able to see if another user issues an `UPDATE user SET password=PASSWORD('not_secure')' query. `mysqld' saves an extra connection for users who have the *process* privilege, so that a *MySQL* `root' user can log in and check things even if all normal connections are in use. * Don't give the *file* privilege to all users. Any user that has this privilege can write a file anywhere in the file system with the privileges of the `mysqld' daemon! To make this a bit safer, all files generated with `SELECT ... INTO OUTFILE' are readable to everyone, and you can't overwrite existing files. The *file* privilege may also be used to read any file accessible to the Unix user that the server runs as. This could be abused, for example, by using `LOAD DATA' to load `/etc/passwd' into a table, which can then be read with `SELECT'. * If you don't trust your DNS, you should use IP numbers instead of hostnames in the grant tables. In principle, the `--secure' option to `mysqld' should make hostnames safe. In any case, you should be very careful about using hostname values that contain wildcards! The following `mysqld' options affect security: `--secure' IP numbers returned by the `gethostbyname()' system call are checked to make sure they resolve back to the original hostname. This makes it harder for someone on the outside to get access by simulating another host. This option also adds some sanity checks of hostnames. The option is turned off by default in *MySQL* 3.21 since it sometimes takes a long time to perform backward resolutions. *MySQL* 3.22 caches hostnames and has this option enabled by default. `--skip-grant-tables' This option causes the server not to use the privilege system at all. This gives everyone *full access* to all databases! (You can tell a running server to start using the grant tables again by executing `mysqladmin reload'.) `--skip-name-resolve' Hostnames are not resolved. All `Host' column values in the grant tables must be IP numbers or `localhost'. `--skip-networking' Don't allow TCP/IP connections over the network. All connections to `mysqld' must be made via Unix sockets. This option is unsuitable for systems that use MIT-pthreads, because the MIT-pthreads package doesn't support Unix sockets. MySQL language reference ************************ Literals: how to write strings and numbers ========================================== Strings ------- A string is a sequence of characters, surrounded by either single quote (`'') or double quote (`"') characters. Examples: 'a string' "another string" Within a string, certain sequences have special meaning. Each of these sequences begins with a backslash (`\'), known as the *escape character*. *MySQL* recognizes the following escape sequences: `\0' An ASCII 0 (`NUL') character. `\n' A newline character. `\t' A tab character. `\r' A carriage return character. `\b' A backspace character. `\'' A single quote (`'') character. `\"' A double quote (`"') character. `\\' A backslash (`\') character. `\%' A `%' character. This is used to search for literal instances of `%' in contexts where `%' would otherwise be interpreted as a wildcard character. `\_' A `_' character. This is used to search for literal instances of `_' in contexts where `_' would otherwise be interpreted as a wildcard character. Note that if you use `\%' or `\%_' in some string contexts, these will return the strings `\%' and `\_' and not `%' and `_'. There are several ways to include quotes within a string: * A `'' inside a string quoted with `'' may be written as `'''. * A `"' inside a string quoted with `"' may be written as `""'. * You can precede the quote character with an escape character (`\'). * A `'' inside a string quoted with `"' needs no special treatment and need not be doubled or escaped. In the same way, `"' inside a string quoted with `'' needs no special treatment. The `SELECT' statements shown below demonstrate how quoting and escaping work: mysql> SELECT 'hello', '"hello"', '""hello""', 'hel''lo', '\'hello'; +-------+---------+-----------+--------+--------+ | hello | "hello" | ""hello"" | hel'lo | 'hello | +-------+---------+-----------+--------+--------+ mysql> SELECT "hello", "'hello'", "''hello''", "hel""lo", "\"hello"; +-------+---------+-----------+--------+--------+ | hello | 'hello' | ''hello'' | hel"lo | "hello | +-------+---------+-----------+--------+--------+ mysql> SELECT "This\nIs\nFour\nlines"; +--------------------+ | This Is Four lines | +--------------------+ If you want to insert binary data into a `BLOB' column, the following characters must be represented by escape sequences: `NUL' ASCII 0. You should represent this by `\0' (a backslash and an ASCII `0' character). `\' ASCII 92, backslash. Represent this by `\\'. `'' ASCII 39, single quote. Represent this by `\''. `"' ASCII 34, double quote. Represent this by `\"'. If you write C code, you can use the C API function `mysql_escape_string()' to escape characters for the `INSERT' statement. *Note C API function overview::. In Perl, you can use the `quote' method of the `DBI' package to convert special characters to the proper escape sequences. *Note Perl `DBI' Class: Perl DBI Class. You should use an escape function on any string that might contain any of the special characters listed above! Numbers ------- Integers are represented as a sequence of digits. Floats use `.' as a decimal separator. Either type of number may be preceded by `-' to indicate a negative value. Examples of valid integers: 1221 0 -32 Examples of valid floating-point numbers: 294.42 -32032.6809e+10 148.00 An integer may be used in a floating-point context; it is interpreted as the equivalent floating-point number. Hexadecimal values ------------------ *MySQL* supports hexadecimal values. In number context these acts like an integer (64 bit precision). In string context these acts like a binary string where each pair of hex digits is converted to a character. mysql> SELECT 0xa+0 -> 10 mysql> select 0x5061756c; -> Paul Hexadecimal strings is often used by ODBC to give values for BLOB columns. `NULL' values ------------- The `NULL' value means "no data" and is different from values such as `0' for numeric types or the empty string for string types. *Note Problems with `NULL': Problems with NULL. `NULL' may be represented by `\N' when using the text file import or export formats (`LOAD DATA INFILE', `SELECT ... INTO OUTFILE'). *Note `LOAD DATA': LOAD DATA. Database, table, index, column and alias names ---------------------------------------------- Database, table, index, column and alias names all follow the same rules in *MySQL*: * A name may consist of alphanumeric characters from the current character set and also `_' and `$'. The default character set is ISO-8859-1 Latin1; this may be changed by recompiling *MySQL*. *Note Character sets::. * A database, table, index or column name can be up to 64 characters long. An alias name can be up to 256 characters long. * A name may start with any character that is legal in a name. In particular, a name may start with a number (this differs from many other database systems!). However, a name cannot consist *only* of numbers. * It is recommended that you do not use names like `1e', because an expression like `1e+1' is ambiguous. It may be interpreted as the expression `1e + 1' or as the number `1e+1'. * You cannot use the `.' character in names because it is used to extend the format by which you can refer to columns (see immediately below). In *MySQL* you can refer to a column using any of the following forms: *Column reference* *Meaning* `col_name' Column `col_name' from whichever table used in the query contains a column of that name `tbl_name.col_name' Column `col_name' from table `tbl_name' of the current database `db_name.tbl_name.col_name'Column `col_name' from table `tbl_name' of the database `db_name'. This form is available in *MySQL* 3.22 or later. You need not specify a `tbl_name' or `db_name.tbl_name' prefix for a column reference in a statement unless the reference would be ambiguous. For example, suppose tables `t1' and `t2' each contain a column `c', and you retrieve `c' in a `SELECT' statement that uses both `t1' and `t2'. In this case, `c' is ambiguous because it is not unique among the tables used in the statement, so you must indicate which table you mean by writing `t1.c' or `t2.c'. Similarly, if you are retrieving from a table `t' in database `db1' and from a table `t' in database `db2', you must refer to columns in those tables as `db1.t.col_name' and `db2.t.col_name'. The syntax `.tbl_name' means the table `tbl_name' in the current database. This syntax is accepted for ODBC compatibility, because some ODBC programs prefix table names with a `.' character. Case sensitivity in names ......................... In *MySQL*, databases and tables correspond to directories and files within those directories. Consequently, the case sensitivity of the underlying operating system determines the case sensitivity of database and table names. This means database and table names are case sensitive in Unix and case insensitive in Win32. *Note:* Although database and table names are case insensitive for Win32, you should not refer to a given database or table using different cases within the same query. The following query would not work because it refers to a table both as `my_table' and as `MY_TABLE': mysql> SELECT * FROM my_table WHERE MY_TABLE.col=1; Column names are case insensitive in all cases. Aliases on tables are case sensitive. The following query would not work because it refers to the alias both as `a' and as `A': mysql> SELECT col_name FROM tbl_name AS a WHERE a.col_name = 1 OR A.col_name = 2; Aliases on columns are case insensitive. Column types ============ *MySQL* supports a number of column types, which may be grouped into three categories: numeric types, date and time types, and string (character) types. This section first gives an overview of the types available and summarizes the storage requirements for each column type, then provides a more detailed description of the properties of the types in each category. The overview is intentionally brief. The more detailed descriptions should be consulted for additional information about particular column types, such as the allowable formats in which you can specify values. The column types supported by *MySQL* are listed below. The following code letters are used in the descriptions: `M' Indicates the maximum display size. The maximum legal display size is 255. `D' Applies to floating-point types and indicates the number of digits following the decimal point. The maximum possible value is 30, but should be no greater than `M'-2. Square brackets (`[' and `]') indicate parts of type specifiers that are optional. Note that if you specify `ZEROFILL' for a column, *MySQL* will automatically add the `UNSIGNED' attribute to the column. `TINYINT[(M)] [UNSIGNED] [ZEROFILL]' A very small integer. The signed range is `-128' to `127'. The unsigned range is `0' to `255'. `SMALLINT[(M)] [UNSIGNED] [ZEROFILL]' A small integer. The signed range is `-32768' to `32767'. The unsigned range is `0' to `65535'. `MEDIUMINT[(M)] [UNSIGNED] [ZEROFILL]' A medium-size integer. The signed range is `-8388608' to `8388607'. The unsigned range is `0' to `16777215'. `INT[(M)] [UNSIGNED] [ZEROFILL]' A normal-size integer. The signed range is `-2147483648' to `2147483647'. The unsigned range is `0' to `4294967295'. `INTEGER[(M)] [UNSIGNED] [ZEROFILL]' This is a synonym for `INT'. `BIGINT[(M)] [UNSIGNED] [ZEROFILL]' A large integer. The signed range is `-9223372036854775808' to `9223372036854775807'. The unsigned range is `0' to `18446744073709551615'. Note that all arithmetic is done using signed `BIGINT' or `DOUBLE' values, so you shouldn't use unsigned big integers larger than `9223372036854775807' (63 bits) except with bit functions! Note that `-', `+' and `*' will use `BIGINT' arithmetic when both arguments are `INTEGER' values! This means that if you multiply two big integers (or results from functions that return integers) you may get unexpected results if the result is larger than `9223372036854775807'. `FLOAT(precision) [ZEROFILL]' A floating-point number. Cannot be unsigned. `precision' can be `4' or `8'. `FLOAT(4)' is a single-precision number and `FLOAT(8)' is a double-precision number. These types are like the `FLOAT' and `DOUBLE' types described immediately below. `FLOAT(4)' and `FLOAT(8)' have the same ranges as the corresponding `FLOAT' and `DOUBLE' types, but their display size and number of decimals is undefined. In *MySQL* 3.23, this is a true floating point value. In earlier *MySQL* versions, `FLOAT(precision)' always has 2 decimals. This syntax is provided for ODBC compatibility. `FLOAT[(M,D)] [ZEROFILL]' A small (single-precision) floating-point number. Cannot be unsigned. Allowable values are `-3.402823466E+38' to `-1.175494351E-38', `0' and `1.175494351E-38' to `3.402823466E+38'. `DOUBLE[(M,D)] [ZEROFILL]' A normal-size (double-precision) floating-point number. Cannot be unsigned. Allowable values are `-1.7976931348623157E+308' to `-2.2250738585072014E-308', `0' and `2.2250738585072014E-308' to `1.7976931348623157E+308'. `DOUBLE PRECISION[(M,D)] [ZEROFILL]' `REAL[(M,D)] [ZEROFILL]' These are synonyms for `DOUBLE'. `DECIMAL(M,D) [ZEROFILL]' An unpacked floating-point number. Cannot be unsigned. Behaves like a `CHAR' column: "unpacked" means the number is stored as a string, using one character for each digit of the value, the decimal point, and, for negative numbers, the `-' sign. If `D' is 0, values will have no decimal point or fractional part. The maximum range of `DECIMAL' values is the same as for `DOUBLE', but the actual range for a given `DECIMAL' column may be constrained by the choice of `M' and `D'. In *MySQL* 3.23 the `M' argument no longer includes the sign or the decimal point. (This is according to ANSI SQL.) `NUMERIC(M,D) [ZEROFILL]' This is a synonym for `DECIMAL'. `DATE' A date. The supported range is `'1000-01-01'' to `'9999-12-31''. *MySQL* displays `DATE' values in `'YYYY-MM-DD'' format, but allows you to assign values to `DATE' columns using either strings or numbers. `DATETIME' A date and time combination. The supported range is `'1000-01-01 00:00:00'' to `'9999-12-31 23:59:59''. *MySQL* displays `DATETIME' values in `'YYYY-MM-DD HH:MM:SS'' format, but allows you to assign values to `DATETIME' columns using either strings or numbers. `TIMESTAMP[(M)]' A timestamp. The range is `'1970-01-01 00:00:00'' to sometime in the year `2037'. *MySQL* displays `TIMESTAMP' values in `YYYYMMDDHHMMSS', `YYMMDDHHMMSS', `YYYYMMDD' or `YYMMDD' format, depending on whether `M' is `14' (or missing), `12', `8' or `6', but allows you to assign values to `TIMESTAMP' columns using either strings or numbers. A `TIMESTAMP' column is useful for recording the date and time of an `INSERT' or `UPDATE' operation because it is automatically set to the date and time of the most recent operation if you don't give it a value yourself. You can also set it to the current date and time by assigning it a `NULL' value. *Note Date and time types::. `TIME' A time. The range is `'-838:59:59'' to `'838:59:59''. *MySQL* displays `TIME' values in `'HH:MM:SS'' format, but allows you to assign values to `TIME' columns using either strings or numbers. `YEAR' A year. The allowable values are `1901' to `2155', and `0000'. *MySQL* displays `YEAR' values in `YYYY' format, but allows you to assign values to `YEAR' columns using either strings or numbers. (The `YEAR' type is new in *MySQL* 3.22.) `CHAR(M) [BINARY]' A fixed-length string that is always right-padded with spaces to the specified length when stored. The range of `M' is 1 to 255 characters. Trailing spaces are removed when the value is retrieved. `CHAR' values are sorted and compared in case-insensitive fashion unless the `BINARY' keyword is given. `VARCHAR(M) [BINARY]' A variable-length string. Note: Trailing spaces are removed when the value is stored (this differs from the ANSI SQL specification). The range of `M' is 1 to 255 characters. `VARCHAR' values are sorted and compared in case-insensitive fashion unless the `BINARY' keyword is given. *Note Silent column changes::. `TINYBLOB' `TINYTEXT' A `BLOB' or `TEXT' column with a maximum length of 255 (2^8 - 1) characters. *Note Silent column changes::. `BLOB' `TEXT' A `BLOB' or `TEXT' column with a maximum length of 65535 (2^16 - 1) characters. *Note Silent column changes::. `MEDIUMBLOB' `MEDIUMTEXT' A `BLOB' or `TEXT' column with a maximum length of 16777215 (2^24 - 1) characters. *Note Silent column changes::. `LONGBLOB' `LONGTEXT' A `BLOB' or `TEXT' column with a maximum length of 4294967295 (2^32 - 1) characters. *Note Silent column changes::. `ENUM('value1','value2',...)' An enumeration. A string object that can have only one value, chosen from the list of values `'value1'', `'value2'', `...', or `NULL'. An `ENUM' can have a maximum of 65535 distinct values. `SET('value1','value2',...)' A set. A string object that can have zero or more values, each of which must be chosen from the list of values `'value1'', `'value2'', `...' A `SET' can have a maximum of 64 members. Column type storage requirements -------------------------------- The storage requirements for each of the column types supported by *MySQL* are listed below by category. Numeric types ------------- *Column type* *Storage required* `TINYINT' 1 byte `SMALLINT' 2 bytes `MEDIUMINT' 3 bytes `INT' 4 bytes `INTEGER' 4 bytes `BIGINT' 8 bytes `FLOAT(4)' 4 bytes `FLOAT(8)' 8 bytes `FLOAT' 4 bytes `DOUBLE' 8 bytes `DOUBLE PRECISION' 8 bytes `REAL' 8 bytes `DECIMAL(M,D)' `M' bytes (`D'+2, if `M < D') `NUMERIC(M,D)' `M' bytes (`D'+2, if `M < D') Date and time types ------------------- *Column type* *Storage required* `DATE' 3 bytes `DATETIME' 8 bytes `TIMESTAMP' 4 bytes `TIME' 3 bytes `YEAR' 1 byte String types ------------ *Column type* *Storage required* `CHAR(M)' `M' bytes, `1 <= M <= 255' `VARCHAR(M)' `L'+1 bytes, where `L <= M' and `1 <= M <= 255' `TINYBLOB', `TINYTEXT' `L'+1 bytes, where `L' < 2^8 `BLOB', `TEXT' `L'+2 bytes, where `L' < 2^16 `MEDIUMBLOB', `L'+3 bytes, where `L' < 2^24 `MEDIUMTEXT' `LONGBLOB', `LONGTEXT' `L'+4 bytes, where `L' < 2^32 `ENUM('value1','value2',...)'1 or 2 bytes, depending on the number of enumeration values (65535 values maximum) `SET('value1','value2',...)'1, 2, 3, 4 or 8 bytes, depending on the number of set members (64 members maximum) `VARCHAR' and the `BLOB' and `TEXT' types are variable-length types, for which the storage requirements depend on the actual length of column values (represented by `L' in the preceding table), rather than on the type's maximum possible size. For example, a `VARCHAR(10)' column can hold a string with a maximum length of 10 characters. The actual storage required is the length of the string (`L'), plus 1 byte to record the length of the string. For the string `'abcd'', `L' is 4 and the storage requirement is 5 bytes. The `BLOB' and `TEXT' types require 1, 2, 3 or 4 bytes to record the length of the column value, depending on the maximum possible length of the type. If a table includes any variable-length column types, the record format will also be variable-length. Note that when a table is created, *MySQL* may under certain conditions change a column from a variable-length type to a fixed-length type, or vice-versa. *Note Silent column changes::. The size of an `ENUM' object is determined by the number of different enumeration values. 1 byte is used for enumerations with up to 255 possible values. 2 bytes are used for enumerations with up to 65535 values. The size of a `SET' object is determined by the number of different set members. If the set size is `N', the object occupies `(N+7)/8' bytes, rounded up to 1, 2, 3, 4 or 8 bytes. A `SET' can have a maximum of 64 members. Numeric types ------------- All integer types can have an optional attribute `UNSIGNED'. Unsigned values can be used when you want to allow only positive numbers in a column and you need a little bigger numeric range for the column. All numeric types can have an optional attribute `ZEROFILL'. Values for `ZEROFILL' columns are left-padded with zeroes up to the maximum display length when they are displayed. For example, for a column declared as `INT(5) ZEROFILL', a value of `4' is retrieved as `00004'. When asked to store a value in a numeric column that is outside the column type's allowable range, *MySQL* clips the value to the appropriate endpoint of the range and stores the resulting value instead. For example, the range of an `INT' column is `-2147483648' to `2147483647'. If you try to insert `-9999999999' into an `INT' column, the value is clipped to the lower endpoint of the range, and `-2147483648' is stored instead. Similarly, if you try to insert `9999999999', `2147483647' is stored instead. If the `INT' column is `UNSIGNED', the size of the column's range is the same but its endpoints shift up to `0' and `4294967295'. If you try to store `-9999999999' and `9999999999', the values stored in the column become `0' and `4294967296'. Conversions that occur due to clipping are reported as "warnings" for `ALTER TABLE', `LOAD DATA INFILE', `UPDATE' and multi-row `INSERT' statements. The maximum display size (`M') and number of decimals (`D') are used for formatting and calculation of maximum column width. *MySQL* will store any value that fits a column's storage type even if the value exceeds the display size. For example, an `INT(4)' column has a display size of 4. Suppose you insert a value which has more than 4 digits into the column, such as `12345'. The display size is exceeded, but the allowable range of the `INT' type is not, so *MySQL* stores the actual value, `12345'. When retrieving the value from the column, *MySQL* returns the actual value stored in the column. Note that if you store bigger values than the display width in a column, you may experience problems when *MySQL* generates temporary tables for some complicated joins as in these case *MySQL* trust that the data did fit into the original column width. The `DECIMAL' type is considered a numeric type (as is its synonym, `NUMERIC'), but such values are stored as strings. One character is used for each digit of the value, the decimal point (if `D' > 0) and the `-' sign (for negative numbers). If `D' is 0, `DECIMAL' and `NUMERIC' values contain no decimal point or fractional part. The maximum range of `DECIMAL' values is the same as for `DOUBLE', but the actual range for a given `DECIMAL' column may be constrained by the choice of `M' and `D'. For example, a type specification such as `DECIMAL(4,2)' indicates a maximum length of four characters with two digits after the decimal point. Due to the way the `DECIMAL' type is stored, this specification results in an allowable range of `-.99' to `9.99', much less than the range of a `DOUBLE'. To avoid some rounding problems, *MySQL* always rounds everything that it stores in any floating-point column to the number of decimals indicated by the column specification. Suppose you have a column type of `FLOAT(8,2)'. The number of decimals is 2, so a value such as `2.333' is rounded to two decimals and stored as `2.33'. Date and time types ------------------- The date and time types are `DATETIME', `DATE', `TIMESTAMP', `TIME' and `YEAR'. Each of these has a range of legal values, as well as a "zero" value that is used when you specify an illegal value. Here are some general considerations to keep in mind when working with date and time types: * *MySQL* retrieves values for a given date or time type in a standard format, but it attempts to interpret a variety of formats for values that you supply (e.g., when you specify a value to be assigned to or compared to a date or time type). Nevertheless, only the formats described in the following sections are supported. It is expected that you will supply legal values, and unpredictable results may occur if you use values in other formats. * Although *MySQL* tries to interpret values in several formats, it always expects the year part of date values to be leftmost. Dates must be given in year-month-day order (e.g., `'98-09-04''), rather than in the month-day-year or day-month-year orders commonly used elsewhere (e.g., `'09-04-98'', `'04-09-98''). * *MySQL* automatically converts a date or time type value to a number if the value is used in a numeric context, and vice versa. * When *MySQL* encounters a value for a date or time type that is out of range or otherwise illegal for the type, it converts the value to the "zero" value for that type. (The exception is that out-of-range `TIME' values are clipped to the appropriate endpoint of the `TIME' range.) The table below shows the format of the "zero" value for each type: *Column type* *"Zero" value* `DATETIME' `'0000-00-00 00:00:00'' `DATE' `'0000-00-00'' `TIMESTAMP' `00000000000000' (length depends on display size) `TIME' `'00:00:00'' `YEAR' `0000' * The "zero" values are special, but you can store or refer to them explicitly using the values shown in the table. You can also do this using the values `'0'' or `0', which are easier to write. * "Zero" date or time values used through *MyODBC* are converted automatically to `NULL' in *MyODBC* 2.50.12 and above, because ODBC can't handle such values. Y2K issues and date types ......................... *MySQL* itself is Y2K-safe (*note Year 2000 compliance::.), but input values presented to *MySQL* may not be. Any input containing 2-digit year values is ambiguous, since the century is unknown. Such values must be interpreted into 4-digit form since *MySQL* stores years internally using four digits. For `DATETIME', `DATE', `TIMESTAMP' and `YEAR' types, *MySQL* interprets dates with ambiguous year values using the following rules: * Year values in the range `00-69' are converted to `2000-2069'. * Year values in the range `70-99' are converted to `1970-1999'. Remember that these rules provide only reasonable guesses as to what your data mean. If the heuristics used by *MySQL* don't produce the correct values, you should provide unambiguous input containing 4-digit year values. The `DATETIME', `DATE' and `TIMESTAMP' types ............................................ The `DATETIME', `DATE' and `TIMESTAMP' types are related. This section describes their characteristics, how they are similar and how they differ. The `DATETIME' type is used when you need values that contain both date and time information. *MySQL* retrieves and displays `DATETIME' values in `'YYYY-MM-DD HH:MM:SS'' format. The supported range is `'1000-01-01 00:00:00'' to `'9999-12-31 23:59:59''. ("Supported" means that although earlier values might work, there is no guarantee that they will.) The `DATE' type is used when you need only a date value, without a time part. *MySQL* retrieves and displays `DATE' values in `'YYYY-MM-DD'' format. The supported range is `'1000-01-01'' to `'9999-12-31''. The `TIMESTAMP' column type provides a type that you can use to automatically mark `INSERT' or `UPDATE' operations with the current date and time. If you have multiple `TIMESTAMP' columns, only the first one is updated automatically. Automatic updating of the first `TIMESTAMP' column occurs under any of the following conditions: * The column is not specified explicitly in an `INSERT' or `LOAD DATA INFILE' statement. * The column is not specified explicitly in an `UPDATE' statement and some other column changes value. (Note that an `UPDATE' that sets a column to the value it already has will not cause the `TIMESTAMP' column to be updated, because if you set a column to its current value, *MySQL* ignores the update for efficiency.) * You explicitly set the `TIMESTAMP' column to `NULL'. `TIMESTAMP' columns other than the first may also be set to the current date and time. Just set the column to `NULL', or to `NOW()'. You can set any `TIMESTAMP' column to a value different than the current date and time by setting it explicitly to the desired value. This is true even for the first `TIMESTAMP' column. You can use this property if, for example, you want a `TIMESTAMP' to be set to the current date and time when you create a row, but not to be changed whenever the row is updated later: * Let *MySQL* set the column when the row is created. This will initialize it to the current date and time. * When you perform subsequent updates to other columns in the row, set the `TIMESTAMP' column explicitly to its current value. On the other hand, you may find it just as easy to use a `DATETIME' column that you initialize to `NOW()' when the row is created and leave alone for subsequent updates. `TIMESTAMP' values may range from the beginning of 1970 to sometime in the year 2037, with a resolution of one second. Values are displayed as numbers. The format in which *MySQL* retrieves and displays `TIMESTAMP' values depends on the display size, as illustrated by the table below. The `full' `TIMESTAMP' format is 14 digits, but `TIMESTAMP' columns may be created with shorter display sizes: *Column type* *Display format* `TIMESTAMP(14)' `YYYYMMDDHHMMSS' `TIMESTAMP(12)' `YYMMDDHHMMSS' `TIMESTAMP(10)' `YYMMDDHHMM' `TIMESTAMP(8)' `YYYYMMDD' `TIMESTAMP(6)' `YYMMDD' `TIMESTAMP(4)' `YYMM' `TIMESTAMP(2)' `YY' All `TIMESTAMP' columns have the same storage size, regardless of display size. The most common display sizes are 6, 8, 12, and 14. You can specify an arbitrary display size at table creation time, but values of 0 or greater than 14 are coerced to 14. Odd-valued sizes in the range from 1 to 13 are coerced to the next higher even number. You can specify `DATETIME', `DATE' and `TIMESTAMP' values using any of a common set of formats: * As a string in either `'YYYY-MM-DD HH:MM:SS'' or `'YY-MM-DD HH:MM:SS'' format. A "relaxed" syntax is allowed--any punctuation character may be used as the delimiter between date parts or time parts. For example, `'98-12-31 11:30:45'', `'98.12.31 11+30+45'', `'98/12/31 11*30*45'' and `'98@12@31 11^30^45'' are equivalent. * As a string in either `'YYYY-MM-DD'' or `'YY-MM-DD'' format. A "relaxed" syntax is allowed here, too. For example, `'98-12-31'', `'98.12.31'', `'98/12/31'' and `'98@12@31'' are equivalent. * As a string with no delimiters in either `'YYYYMMDDHHMMSS'' or `'YYMMDDHHMMSS'' format, provided that the string makes sense as a date. For example, `'19970523091528'' and `'970523091528'' are interpreted as `'1997-05-23 09:15:28'', but `'971122459015'' is illegal (it has a nonsensical minute part) and becomes `'0000-00-00 00:00:00''. * As a string with no delimiters in either `'YYYYMMDD'' or `'YYMMDD'' format, provided that the string makes sense as a date. For example, `'19970523'' and `'970523'' are interpreted as `'1997-05-23'', but `'971332'' is illegal (it has nonsensical month and day parts) and becomes `'0000-00-00''. * As a number in either `YYYYMMDDHHMMSS' or `YYMMDDHHMMSS' format, provided that the number makes sense as a date. For example, `19830905132800' and `830905132800' are interpreted as `'1983-09-05 13:28:00''. * As a number in either `YYYYMMDD' or `YYMMDD' format, provided that the number makes sense as a date. For example, `19830905' and `830905' are interpreted as `'1983-09-05''. * As the result of a function that returns a value that is acceptable in a `DATETIME', `DATE' or `TIMESTAMP' context, such as `NOW()' or `CURRENT_DATE'. Illegal `DATETIME', `DATE' or `TIMESTAMP' values are converted to the "zero" value of the appropriate type (`'0000-00-00 00:00:00'', `'0000-00-00'' or `00000000000000'). For values specified as strings that include date part delimiters, it is not necessary to specify two digits for month or day values that are less than `10'. `'1979-6-9'' is the same as `'1979-06-09''. Similarly, for values specified as strings that include time part delimiters, it is not necessary to specify two digits for hour, month or second values that are less than `10'. `'1979-10-30 1:2:3'' is the same as `'1979-10-30 01:02:03''. Values specified as numbers should be 6, 8, 12 or 14 digits long. If the number is 8 or 14 digits long, it is assumed to be in `YYYYMMDD' or `YYYYMMDDHHMMSS' format and that the year is given by the first 4 digits. If the number is 6 or 12 digits long, it is assumed to be in `YYMMDD' or `YYMMDDHHMMSS' format and that the year is given by the first 2 digits. Numbers that are not one of these lengths are interpreted as though padded with leading zeros to the closest length. Values specified as non-delimited strings are interpreted using their length as given. If the string is 8 or 14 characters long, the year is assumed to be given by the first 4 characters. Otherwise the year is assumed to be given by the first 2 characters. The string is interpreted from left to right to find year, month, day, hour, minute and second values, for as many parts as are present in the string. This means you should not use strings that have fewer than 6 characters. For example, if you specify `'9903'', thinking that will represent March, 1999, you will find that *MySQL* inserts a "zero" date into your table. This is because the year and month values are `99' and `03', but the day part is missing (zero), so the value is not a legal date. `TIMESTAMP' columns store legal values using the full precision with which the value was specified, regardless of the display size. This has several implications: * Always specify year, month, and day, even if your column types are `TIMESTAMP(4)' or `TIMESTAMP(2)'. Otherwise, the value will not be a legal date and `0' will be stored. * If you use `ALTER TABLE' to widen a narrow `TIMESTAMP' column, information will be displayed that previously was "hidden". * Similarly, narrowing a `TIMESTAMP' column does not cause information to be lost, except in the sense that less information is shown when the values are displayed. * Although `TIMESTAMP' values are stored to full precision, the only function that operates directly on the underlying stored value is `UNIX_TIMESTAMP()'. Other functions operate on the formatted retrieved value. This means you cannot use functions such as `HOUR()' or `SECOND()' unless the relevant part of the `TIMESTAMP' value is included in the formatted value. For example, the `HH' part of a `TIMESTAMP' column is not displayed unless the display size is at least 10, so trying to use `HOUR()' on shorter `TIMESTAMP' values produces a meaningless result. You can to some extent assign values of one date type to an object of a different date type. However, there may be some alteration of the value or loss of information: * If you assign a `DATE' value to a `DATETIME' or `TIMESTAMP' object, the time part of the resulting value is set to `'00:00:00'', because the `DATE' value contains no time information. * If you assign a `DATETIME' or `TIMESTAMP' value to a `DATE' object, the time part of the resulting value is deleted, because the `DATE' type stores no time information. * Remember that although `DATETIME', `DATE' and `TIMESTAMP' values all can be specified using the same set of formats, the types do not all have the same range of values. For example, `TIMESTAMP' values cannot be earlier than `1970' or later than `2037'. This means that a date such as `'1968-01-01'', while legal as a `DATETIME' or `DATE' value, is not a valid `TIMESTAMP' value and will be converted to `0' if assigned to such an object. Be aware of certain pitfalls when specifying date values: * The relaxed format allowed for values specified as strings can be deceiving. For example, a value such as `'10:11:12'' might look like a time value because of the `:' delimiter, but if used in a date context will be interpreted as the year `'2010-11-12''. The value `'10:45:15'' will be converted to `'0000-00-00'' because `'45'' is not a legal month. * Year values specified as two digits are ambiguous, since the century is unknown. *MySQL* interprets 2-digit year values using the following rules: - Year values in the range `00-69' are converted to `2000-2069'. - Year values in the range `70-99' are converted to `1970-1999'. The `TIME' type ............... *MySQL* retrieves and displays `TIME' values in `'HH:MM:SS'' format (or `'HHH:MM:SS'' format for large hours values). `TIME' values may range from `'-838:59:59'' to `'838:59:59''. The reason the hours part may be so large is that the `TIME' type may be used not only to represent a time of day (which must be less than 24 hours), but also elapsed time or a time interval between two events (which may be much greater than 24 hours, or even negative). You can specify `TIME' values in a variety of formats: * As a string in `'HH:MM:SS'' format. A "relaxed" syntax is allowed--any punctuation character may be used as the delimiter between time parts. For example, `'10:11:12'' and `'10.11.12'' are equivalent. * As a string with no delimiters in `'HHMMSS'' format, provided that it makes sense as a time. For example, `'101112'' is understood as `'10:11:12'', but `'109712'' is illegal (it has a nonsensical minute part) and becomes `'00:00:00''. * As a number in `HHMMSS' format, provided that it makes sense as a time. For example, `101112' is understood as `'10:11:12''. * As the result of a function that returns a value that is acceptable in a `TIME' context, such as `CURRENT_TIME'. For `TIME' values specified as strings that include a time part delimiter, it is not necessary to specify two digits for hours, minutes or seconds values that are less than `10'. `'8:3:2'' is the same as `'08:03:02''. Be careful about assigning "short" `TIME' values to a `TIME' column. *MySQL* interprets values using the assumption that the rightmost digits represent seconds. (*MySQL* interprets `TIME' values as elapsed time, rather than as time of day.) For example, you might think of `'11:12'', `'1112'' and `1112' as meaning `'11:12:00'' (12 minutes after 11 o'clock), but *MySQL* interprets them as `'00:11:12'' (11 minutes, 12 seconds). Similarly, `'12'' and `12' are interpreted as `'00:00:12''. Values that lie outside the `TIME' range but are otherwise legal are clipped to the appropriate endpoint of the range. For example, `'-850:00:00'' and `'850:00:00'' are converted to `'-838:59:59'' and `'838:59:59''. Illegal `TIME' values are converted to `'00:00:00''. Note that since `'00:00:00'' is itself a legal `TIME' value, there is no way to tell, from a value of `'00:00:00'' stored in a table, whether the original value was specified as `'00:00:00'' or whether it was illegal. The `YEAR' type ............... The `YEAR' type is a 1-byte type used for representing years. *MySQL* retrieves and displays `YEAR' values in `YYYY' format. The range is `1901' to `2155'. You can specify `YEAR' values in a variety of formats: * As a four-digit string in the range `'1901'' to `'2155''. * As a four-digit number in the range `1901' to `2155'. * As a two-digit string in the range `'00'' to `'99''. Values in the ranges `'00'' to `'69'' and `'70'' to `'99'' are converted to `YEAR' values in the ranges `2000' to `2069' and `1970' to `1999'. * As a two-digit number in the range `1' to `99'. Values in the ranges `1' to `69' and `70' to `99' are converted to `YEAR' values in the ranges `2001' to `2069' and `1970' to `1999'. Note that the range for two-digit numbers is slightly different than the range for two-digit strings, since you cannot specify zero directly as a number and have it be interpreted as `2000'. You *must* specify it as a string `'0'' or `'00'' or it will be interpreted as `0000'. * As the result of a function that returns a value that is acceptable in a `YEAR' context, such as `NOW()'. Illegal `YEAR' values are converted to `0000'. String types ------------ The string types are `CHAR', `VARCHAR', `BLOB', `TEXT', `ENUM' and `SET'. The `CHAR' and `VARCHAR' types .............................. The `CHAR' and `VARCHAR' types are similar, but differ in the way they are stored and retrieved. The length of a `CHAR' column is fixed to the length that you declare when you create the table. The length can be any value between 1 and 255. (As of MySQL 3.23, the length of `CHAR' may be 0 to 255.) When `CHAR' values are stored, they are right-padded with spaces to the specified length. When `CHAR' values are retrieved, trailing spaces are removed. Values in `VARCHAR' columns are variable-length strings. You can declare a `VARCHAR' column to be any length between 1 and 255, just as for `CHAR' columns. However, in contrast to `CHAR', `VARCHAR' values are stored using only as many characters as are needed, plus one byte to record the length. Values are not padded; instead, trailing spaces are removed when values are stored. (This space removal differs from the ANSI SQL specification.) If you assign a value to a `CHAR' or `VARCHAR' column that exceeds the column's maximum length, the value is truncated to fit. The table below illustrates the differences between the two types of columns by showing the result of storing various string values into `CHAR(4)' and `VARCHAR(4)' columns: *Value* `CHAR(4)' *Storage `VARCHAR(4)' *Storage required* required* `''' `' '' 4 bytes `''' 1 byte `'ab'' `'ab '' 4 bytes `'ab'' 3 bytes `'abcd'' `'abcd'' 4 bytes `'abcd'' 5 bytes `'abcdefgh'' `'abcd'' 4 bytes `'abcd'' 5 bytes The values retrieved from the `CHAR(4)' and `VARCHAR(4)' columns will be the same in each case, because trailing spaces are removed from `CHAR' columns upon retrieval. Values in `CHAR' and `VARCHAR' columns are sorted and compared in case-insensitive fashion, unless the `BINARY' attribute was specified when the table was created. The `BINARY' attribute means that column values are sorted and compared in case-sensitive fashion according to the ASCII order of the machine where the *MySQL* server is running. The `BINARY' attribute is "sticky". This means that if a column marked `BINARY' is used in an expression, the whole expression is compared as a `BINARY' value. *MySQL* may silently change the type of a `CHAR' or `VARCHAR' column at table creation time. *Note Silent column changes::. The `BLOB' and `TEXT' types ........................... A `BLOB' is a binary large object that can hold a variable amount of data. The four `BLOB' types `TINYBLOB', `BLOB', `MEDIUMBLOB' and `LONGBLOB' differ only in the maximum length of the values they can hold. *Note Storage requirements::. The four `TEXT' types `TINYTEXT', `TEXT', `MEDIUMTEXT' and `LONGTEXT' correspond to the four `BLOB' types and have the same maximum lengths and storage requirements. The only difference between `BLOB' and `TEXT' types is that sorting and comparison is performed in case-sensitive fashion for `BLOB' values and case-insensitive fashion for `TEXT' values. In other words, a `TEXT' is a case-insensitive `BLOB'. If you assign a value to a `BLOB' or `TEXT' column that exceeds the column type's maximum length, the value is truncated to fit. In most respects, you can regard a `TEXT' column as a `VARCHAR' column that can be as big as you like. Similarly, you can regard a `BLOB' column as a `VARCHAR BINARY' column. The differences are: * You can have indexes on `BLOB' and `TEXT' columns with *MySQL* versions 3.23.2 and newer. Older versions of *MySQL* did not support this. * There is no trailing-space removal for `BLOB' and `TEXT' columns when values are stored, as there is for `VARCHAR' columns. * `BLOB' and `TEXT' columns cannot have `DEFAULT' values. *MyODBC* defines `BLOB' values as `LONGVARBINARY' and `TEXT' values as `LONGVARCHAR'. Because `BLOB' and `TEXT' values may be extremely long, you may run up against some constraints when using them: * If you want to use `GROUP BY' or `ORDER BY' on a `BLOB' or `TEXT' column, you must convert the column value into a fixed-length object. The standard way to do this is with the `SUBSTRING' function. For example: mysql> select comment from tbl_name,substring(comment,20) as substr ORDER BY substr; If you don't do this, only the first `max_sort_length' bytes of the column are used when sorting. The default value of `max_sort_length' is 1024; this value can be changed using the `-O' option when starting the `mysqld' server. You can group on an expression involving `BLOB' or `TEXT' values by specifying the column position or by using an alias: mysql> select id,substring(blob_col,1,100) from tbl_name GROUP BY 2; mysql> select id,substring(blob_col,1,100) as b from tbl_name GROUP BY b; * The maximum size of a `BLOB' or `TEXT' object is determined by its type, but the largest value you can actually transmit between the client and server is determined by the amount of available memory and the size of the communications buffers. You can change the message buffer size, but you must do so on both the server and client ends. *Note Server parameters::. Note that each `BLOB' or `TEXT' value is represented internally by a separately-allocated object. This is in contrast to all other column types, for which storage is allocated once per column when the table is opened. The `ENUM' type ............... An `ENUM' is a string object whose value normally is chosen from a list of allowed values that are enumerated explicitly in the column specification at table creation time. The value may also be the empty string (`""') or `NULL' under certain circumstances: * If you insert an invalid value into an `ENUM' (that is, a string not present in the list of allowed values), the empty string is inserted instead as a special error value. * If an `ENUM' is declared `NULL', `NULL' is also a legal value for the column, and the default value is `NULL'. If an `ENUM' is declared `NOT NULL', the default value is the first element of the list of allowed values. Each enumeration value has an index: * Values from the list of allowable elements in the column specification are numbered beginning with 1. * The index value of the empty string error value is 0. This means that you can use the following `SELECT' statement to find rows into which invalid `ENUM' values were assigned: mysql> SELECT * FROM tbl_name WHERE enum_col=0; * The index of the `NULL' value is `NULL'. For example, a column specified as `ENUM("one", "two", "three")' can have any of the values shown below. The index of each value is also shown: *Value* *Index* `NULL' `NULL' `""' 0 `"one"' 1 `"two"' 2 `"three"' 3 An enumeration can have a maximum of 65535 elements. Lettercase is irrelevant when you assign values to an `ENUM' column. However, values retrieved from the column later have lettercase matching the values that were used to specify the allowable values at table creation time. If you retrieve an `ENUM' in a numeric context, the column value's index is returned. If you store a number into an `ENUM', the number is treated as an index, and the the value stored is the enumeration member with that index. `ENUM' values are sorted according to the order in which the enumeration members were listed in the column specification. (In other words, `ENUM' values are sorted according to their index numbers.) For example, `"a"' sorts before `"b"' for `ENUM("a", "b")', but `"b"' sorts before `"a"' for `ENUM("b", "a")'. The empty string sorts before non-empty strings, and `NULL' values sort before all other enumeration values. If you want to get all possible values for an `ENUM' column, you should use: `SHOW COLUMNS FROM table_name LIKE enum_column_name' and parse the `ENUM' definition in the second column. The `SET' type .............. A `SET' is a string object that can have zero or more values, each of which must be chosen from a list of allowed values specified when the table is created. `SET' column values that consist of multiple set members are specified with members separated by commas (`,'). A consequence of this is that `SET' member values cannot themselves contain commas. For example, a column specified as `SET("one", "two") NOT NULL' can have any of these values: "" "one" "two" "one,two" A `SET' can have a maximum of 64 different members. *MySQL* stores `SET' values numerically, with the low-order bit of the stored value corresponding to the first set member. If you retrieve a `SET' value in a numeric context, the value retrieved has bits set corresponding to the set members that make up the column value. If a number is stored into a `SET' column, the bits that are set in the binary representation of the number determine the set members in the column value. Suppose a column is specified as `SET("a","b","c","d")'. Then the members have the following bit values: `SET' *Decimal *Binary value* *member* value* `a' `1' `0001' `b' `2' `0010' `c' `4' `0100' `d' `8' `1000' If you assign a value of `9' to this column, that is `1001' in binary, so the first and fourth `SET' value members `"a"' and `"d"' are selected and the resulting value is `"a,d"'. For a value containing more than one `SET' element, it does not matter what order the elements are listed in when you insert the value. It also doesn't not matter how many times a given element is listed in the value. When the value is retrieved later, each element in the value will appear once, with elements listed according to the order in which they were specified at table creation time. For example, if a column is specified as `SET("a","b","c","d")', then `"a,d"', `"d,a"' and `"d,a,a,d,d"' will all appear as `"a,d"' when retrieved. `SET' values are sorted numerically. `NULL' values sort before non-`NULL' `SET' values. Normally, you perform a `SELECT' on a `SET' column using the `LIKE' operator or the `FIND_IN_SET()' function: mysql> SELECT * FROM tbl_name WHERE set_col LIKE '%value%'; mysql> SELECT * FROM tbl_name WHERE FIND_IN_SET('value',set_col)>0; But the following will also work: mysql> SELECT * FROM tbl_name WHERE set_col = 'val1,val2'; mysql> SELECT * FROM tbl_name WHERE set_col & 1; The first of these statements looks for an exact match. The second looks for values containing the first set member. If you want to get all possible values for an `SET' column, you should use: `SHOW COLUMNS FROM table_name LIKE set_column_name' and parse the `SET' definition in the second column. Choosing the right type for a column ------------------------------------ For the most efficient use of storage, try to use the most precise type in all cases. For example, if an integer column will be used for values in the range between `1' and `99999', `MEDIUMINT UNSIGNED' is the best type. Accurate representation of monetary values is a common problem. In *MySQL*, you should use the `DECIMAL' type. This is stored as a string, so no loss of accuracy should occur. If accuracy is not too important, the `DOUBLE' type may also be good enough. For high precision, you can always convert to a fixed-point type stored in a `BIGINT'. This allows you to do all calculations with integers and convert results back to floating-point values only when necessary. *Note Row format::. Column indexes -------------- All *MySQL* column types can be indexed. Use of indexes on the relevant columns is the best way to improve the performance of `SELECT' operations. A table may have up to 16 indexes. The maximum index length is 256 bytes, although this may be changed when compiling *MySQL*. For `CHAR' and `VARCHAR' columns, you can index a prefix of a column. This is much faster and requires less disk space than indexing the whole column. The syntax to use in the `CREATE TABLE' statement to index a column prefix looks like this: KEY index_name (col_name(length)) The example below creates an index for the first 10 characters of the `name' column: mysql> CREATE TABLE test ( name CHAR(200) NOT NULL, KEY index_name (name(10))); For `BLOB' and `TEXT' columns, you must index a prefix of the column, you cannot index the entire thing. Multiple-column indexes ----------------------- *MySQL* can create indexes on multiple columns. An index may consist of up to 15 columns. (On `CHAR' and `VARCHAR' columns you can also use a prefix of the column as a part of an index). A multiple-column index can be considered a sorted array containing values that are created by concatenating the values of the indexed columns. *MySQL* uses multiple-column indexes in such a way that queries are fast when you specify a known quantity for the first column of the index in a `WHERE' clause, even if you don't specify values for the other columns. Suppose a table is created using the following specification: mysql> CREATE TABLE test ( id INT NOT NULL, last_name CHAR(30) NOT NULL, first_name CHAR(30) NOT NULL, PRIMARY KEY (id), INDEX name (last_name,first_name)); Then the index `name' is an index over `last_name' and `first_name'. The index will be used for queries that specify values in a known range for `last_name', or for both `last_name' and `first_name'. Therefore, the `name' index will be used in the following queries: mysql> SELECT * FROM test WHERE last_name="Widenius"; mysql> SELECT * FROM test WHERE last_name="Widenius" AND first_name="Michael"; mysql> SELECT * FROM test WHERE last_name="Widenius" AND (first_name="Michael" OR first_name="Monty"); mysql> SELECT * FROM test WHERE last_name="Widenius" AND first_name >="M" AND first_name < "N"; However, the `name' index will NOT be used in the following queries: mysql> SELECT * FROM test WHERE first_name="Michael"; mysql> SELECT * FROM test WHERE last_name="Widenius" OR first_name="Michael"; For more information on the manner in which *MySQL* uses indexes to improve query performance, see *Note *MySQL* indexes: MySQL indexes. Using column types from other database engines ---------------------------------------------- To make it easier to use code written for SQL implementations from other vendors, *MySQL* maps column types as shown in the table below. These mappings make it easier to move table definitions from other database engines to *MySQL*: *Other vendor type* *MySQL type* `BINARY(NUM)' `CHAR(NUM) BINARY' `CHAR VARYING(NUM)' `VARCHAR(NUM)' `FLOAT4' `FLOAT' `FLOAT8' `DOUBLE' `INT1' `TINYINT' `INT2' `SMALLINT' `INT3' `MEDIUMINT' `INT4' `INT' `INT8' `BIGINT' `LONG VARBINARY' `MEDIUMBLOB' `LONG VARCHAR' `MEDIUMTEXT' `MIDDLEINT' `MEDIUMINT' `VARBINARY(NUM)' `VARCHAR(NUM) BINARY' Column type mapping occurs at table creation time. If you create a table with types used by other vendors and then issue a `DESCRIBE tbl_name' statement, *MySQL* reports the table structure using the equivalent *MySQL* types. Functions for use in `SELECT' and `WHERE' clauses ================================================= A `select_expression' or `where_definition' in a SQL statement can consist of any expression using the functions described below. An expression that contains `NULL' always produces a `NULL' value unless otherwise indicated in the documentation for the operators and functions involved in the expression. *Note:* There must be no whitespace between a function name and the parenthesis following it. This helps the *MySQL* parser distinguish between function calls and references to tables or columns that happen to have the same name as a function. Spaces around arguments are permitted, though. For the sake of brevity, examples display the output from the `mysql' program in abbreviated form. So this: mysql> select MOD(29,9); 1 rows in set (0.00 sec) +-----------+ | mod(29,9) | +-----------+ | 2 | +-----------+ Is displayed like this: mysql> select MOD(29,9); -> 2 Grouping functions ------------------ `( ... )' Parentheses. Use these to force the order of evaluation in an expression. mysql> select 1+2*3; -> 7 mysql> select (1+2)*3; -> 9 Normal arithmetic operations ---------------------------- The usual arithmetic operators are available. Note that in the case of `-', `+' and `*', the result is calculated with `BIGINT' (64-bit) precision if both arguments are integers! `+' Addition mysql> select 3+5; -> 8 `-' Subtraction mysql> select 3-5; -> -2 `*' Multiplication mysql> select 3*5; -> 15 mysql> select 18014398509481984*18014398509481984.0; -> 324518553658426726783156020576256.0 mysql> select 18014398509481984*18014398509481984; -> 0 The result of the last expression is incorrect because the result of the integer multiplication exceeds the 64-bit range of `BIGINT' calculations. `/' Division mysql> select 3/5; -> 0.60 Division by zero produces a `NULL' result: mysql> select 102/(1-1); -> NULL A division will be calculated with `BIGINT' arithmetic only if performed in a context where its result is converted to an integer! Bit functions ------------- *MySQL* uses `BIGINT' (64-bit) arithmetic for bit operations, so these operators have a maximum range of 64 bits. `|' Bitwise OR mysql> select 29 | 15; -> 31 `&' Bitwise AND mysql> select 29 & 15; -> 13 `<<' Shifts a longlong (`BIGINT') number to the left. mysql> select 1 << 2 -> 4 `>>' Shifts a longlong (`BIGINT') number to the right. mysql> select 4 >> 2 -> 1 `BIT_COUNT(N)' Returns the number of bits that are set in the argument `N'. mysql> select BIT_COUNT(29); -> 4 Logical operations ------------------ All logical functions return `1' (TRUE) or `0' (FALSE). `NOT' `!' Logical NOT. Returns `1' if the argument is `0', otherwise returns `0'. Exception: `NOT NULL' returns `NULL'. mysql> select NOT 1; -> 0 mysql> select NOT NULL; -> NULL mysql> select ! (1+1); -> 0 mysql> select ! 1+1; -> 1 The last example returns `1' because the expression evaluates the same way as `(!1)+1'. `OR' `||' Logical OR. Returns `1' if either argument is not `0' and not `NULL'. mysql> select 1 || 0; -> 1 mysql> select 0 || 0; -> 0 mysql> select 1 || NULL; -> 1 `AND' `&&' Logical AND. Returns `0' if either argument is `0' or `NULL', otherwise returns `1'. mysql> select 1 && NULL; -> 0 mysql> select 1 && 0; -> 0 Comparison operators -------------------- Comparison operations result in a value of `1' (TRUE), `0' (FALSE) or `NULL'. These functions work for both numbers and strings. Strings are automatically converted to numbers and numbers to strings as needed (as in Perl). *MySQL* performs comparisons using the following rules: * If one or both arguments are `NULL', the result of the comparison is `NULL', except for the `<=>' operator. * If both arguments in a comparison operation are strings, they are compared as strings. * If both arguments are integers, they are compared as integers. * Hexadecimal values are treated as binary strings if not compared to a number. * If one of the arguments is a `TIMESTAMP' or `DATETIME' column and the other argument is a constant, the constant is converted to a timestamp before the comparison is performed. This is done to be more ODBC-friendly. * In all other cases, the arguments are compared as floating-point (real) numbers. By default, string comparisons are done in case-independent fashion using the current character set (ISO-8859-1 Latin1 by default, which also works excellently for English). The examples below illustrate conversion of strings to numbers for comparison operations: mysql> SELECT 1 > '6x'; -> 0 mysql> SELECT 7 > '6x'; -> 1 mysql> SELECT 0 > 'x6'; -> 0 mysql> SELECT 0 = 'x6'; -> 1 `=' Equal mysql> select 1 = 0; -> 0 mysql> select '0' = 0; -> 1 mysql> select '0.0' = 0; -> 1 mysql> select '0.01' = 0; -> 0 mysql> select '.01' = 0.01; -> 1 `<>' `!=' Not equal mysql> select '.01' <> '0.01'; -> 1 mysql> select .01 <> '0.01'; -> 0 mysql> select 'zapp' <> 'zappp'; -> 1 `<=' Less than or equal mysql> select 0.1 <= 2; -> 1 `<' Less than mysql> select 2 <= 2; -> 1 `>=' Greater than or equal mysql> select 2 >= 2; -> 1 `>' Greater than mysql> select 2 > 2; -> 0 `<=>' Null safe equal mysql> select 1 <=> 1, NULL <=> NULL, 1 <=> NULL; -> 1 1 0 `IS NULL' `IS NOT NULL' Test whether or not a value is or is not `NULL' mysql> select 1 IS NULL, 0 IS NULL, NULL IS NULL: -> 0 0 1 mysql> select 1 IS NOT NULL, 0 IS NOT NULL, NULL IS NOT NULL; -> 1 1 0 `expr BETWEEN min AND max' If `expr' is greater than or equal to `min' and `expr' is less than or equal to `max', `BETWEEN' returns `1', otherwise it returns `0'. This is equivalent to the expression `(min <= expr AND expr <= max)' if all the arguments are of the same type. The first argument (`expr') determines how the comparison is performed. If `expr' is a case-insensitive string expression, a case-insensitive string comparison is done. If `expr' is a case-sensitive string expression, a case-sensitive string comparison is done. If `expr' is an integer expression, an integer comparison is done. Otherwise, a floating-point (real) comparison is done. mysql> select 1 BETWEEN 2 AND 3; -> 0 mysql> select 'b' BETWEEN 'a' AND 'c'; -> 1 mysql> select 2 BETWEEN 2 AND '3'; -> 1 mysql> select 2 BETWEEN 2 AND 'x-3'; -> 0 `expr IN (value,...)' Returns `1' if `expr' is any of the values in the `IN' list, else returns `0'. If all values are constants, then all values are evaluated according to the type of `expr' and sorted. The search for the item is then done using a binary search. This means `IN' is very quick if the `IN' value list consists entirely of constants. If `expr' is a case-sensitive string expression, the string comparison is performed in case-sensitive fashion. mysql> select 2 IN (0,3,5,'wefwf'); -> 0 mysql> select 'wefwf' IN (0,3,5,'wefwf'); -> 1 `expr NOT IN (value,...)' Same as `NOT (expr IN (value,...))'. `ISNULL(expr)' If `expr' is `NULL', `ISNULL()' returns `1', otherwise it returns `0'. mysql> select ISNULL(1+1); -> 0 mysql> select ISNULL(1/0); -> 1 Note that a comparison of `NULL' values using `=' will always be false! `COALESCE(list)' Returns first non-`NULL' element in list. mysql> select COALESCE(NULL,1); -> 1 mysql> select COALESCE(NULL,NULL,NULL); -> NULL `INTERVAL(N,N1,N2,N3,...)' Returns `0' if `N' < `N1', `1' if `N' < `N2' and so on. All arguments are treated as integers. It is required that `N1' < `N2' < `N3' < `...' < `Nn' for this function to work correctly. This is because a binary search is used (very fast). mysql> select INTERVAL(23, 1, 15, 17, 30, 44, 200); -> 3 mysql> select INTERVAL(10, 1, 10, 100, 1000); -> 2 mysql> select INTERVAL(22, 23, 30, 44, 200); -> 0 String comparison functions --------------------------- Normally, if any expression in a string comparison is case sensitive, the comparison is performed in case-sensitive fashion. `expr LIKE pat [ESCAPE 'escape-char']' Pattern matching using SQL simple regular expression comparison. Returns `1' (TRUE) or `0' (FALSE). With `LIKE' you can use the following two wildcard characters in the pattern: `%' Matches any number of characters, even zero characters `_' Matches exactly one character mysql> select 'David!' LIKE 'David_'; -> 1 mysql> select 'David!' LIKE '%D%v%'; -> 1 To test for literal instances of a wildcard character, precede the character with the escape character. If you don't specify the `ESCAPE' character, `\' is assumed: `\%' Matches one `%' character `\_' Matches one `_' character mysql> select 'David!' LIKE 'David\_'; -> 0 mysql> select 'David_' LIKE 'David\_'; -> 1 To specify a different escape character, use the `ESCAPE' clause: mysql> select 'David_' LIKE 'David|_' ESCAPE '|'; -> 1 `LIKE' is allowed on numeric expressions! (This is a *MySQL* extension to the ANSI SQL `LIKE'.) mysql> select 10 LIKE '1%'; -> 1 Note: Because *MySQL* uses the C escape syntax in strings (e.g., `\n'), you must double any `\' that you use in your `LIKE' strings. For example, to search for `\n', specify it as `\\n'. To search for `\', specify it as `\\\\' (the backslashes are stripped once by the parser, and another time when the pattern match is done, leaving a single backslash to be matched). `expr NOT LIKE pat [ESCAPE 'escape-char']' Same as `NOT (expr LIKE pat [ESCAPE 'escape-char'])'. `expr REGEXP pat' `expr RLIKE pat' Performs a pattern match of a string expression `expr' against a pattern `pat'. The pattern can be an extended regular expression. *Note Regexp::. Returns `1' if `expr' matches `pat', otherwise returns `0'. `RLIKE' is a synonym for `REGEXP', provided for `mSQL' compatibility. Note: Because *MySQL* uses the C escape syntax in strings (e.g., `\n'), you must double any `\' that you use in your `REGEXP' strings. In `MySQL' 3.23.4 `REGEXP' is case insensitive for normal (not binary) strings. mysql> select 'Monty!' REGEXP 'm%y%%'; -> 0 mysql> select 'Monty!' REGEXP '.*'; -> 1 mysql> select 'new*\n*line' REGEXP 'new\\*.\\*line'; -> 1 mysql> select "a" REGEXP "A", "a" REGEXP BINARY "A"; -> 1 0 `' `REGEXP' and `RLIKE' use the current character set (ISO-8859-1 Latin1 by default) when deciding the type of a character. `expr NOT REGEXP pat' `expr NOT RLIKE pat' Same as `NOT (expr REGEXP pat)'. `STRCMP(expr1,expr2)' `STRCMP()' returns `0' if the strings are the same, `-1' if the first argument is smaller than the second according to the current sort order, and `1' otherwise. mysql> select STRCMP('text', 'text2'); -> -1 mysql> select STRCMP('text2', 'text'); -> 1 mysql> select STRCMP('text', 'text'); -> 0 Cast operators -------------- ``BINARY'' The `BINARY' operator casts the string following it to a binary string. This is an easy way to force a column comparison to be case sensitive even if the column isn't defined as `BINARY' or `BLOB'. mysql> select "a" = "A"; -> 1 mysql> select BINARY "a" = "A"; -> 0 `BINARY' was introduced in *MySQL* 3.23.0 Control flow functions ---------------------- `IFNULL(expr1,expr2)' If `expr1' is not `NULL', `IFNULL()' returns `expr1', else it returns `expr2'. `IFNULL()' returns a numeric or string value, depending on the context in which it is used. mysql> select IFNULL(1,0); -> 1 mysql> select IFNULL(0,10); -> 0 mysql> select IFNULL(1/0,10); -> 10 mysql> select IFNULL(1/0,'yes'); -> 'yes' `IF(expr1,expr2,expr3)' If `expr1' is TRUE (`expr1 <> 0' and `expr1 <> NULL') then `IF()' returns `expr2', else it returns `expr3'. `IF()' returns a numeric or string value, depending on the context in which it is used. mysql> select IF(1>2,2,3); -> 3 mysql> select IF(1<2,'yes','no'); -> 'yes' mysql> select IF(strcmp('test','test1'),'yes','no'); -> 'no' `expr1' is evaluated as an integer value, which means that if you are testing floating-point or string values, you should do so using a comparison operation. mysql> select IF(0.1,1,0); -> 0 mysql> select IF(0.1<>0,1,0); -> 1 In the first case above, `IF(0.1)' returns `0' because `0.1' is converted to an integer value, resulting in a test of `IF(0)'. This may not be what you expect. In the second case, the comparison tests the original floating-point value to see whether it is non-zero. The result of the comparison is used as an integer. `CASE value WHEN [compare-value] THEN result [WHEN [compare-value] THEN result ...] [ELSE result] END' `CASE WHEN [condition] THEN result [WHEN [condition] THEN result ...] [ELSE result] END' The first version returns the `result' where `value=compare-value'. The second version returns the result for the first condition which is true. If there was no matching result value, then the result after `ELSE' is returned. If there is no `ELSE' part then `NULL' is returned. mysql> SELECT CASE 1 WHEN 1 THEN "one" WHEN 2 THEN "two" ELSE "more" END; -> "one" mysql> SELECT CASE WHEN 1>0 THEN "true" ELSE "false" END; -> "true" mysql> SELECT CASE BINARY "B" when "a" then 1 when "b" then 2 END; -> NULL Mathematical functions ---------------------- All mathematical functions return `NULL' in case of an error. `-' Unary minus. Changes the sign of the argument. mysql> select - 2; -> -2 Note that if this operator is used with a `BIGINT', the return value is a `BIGINT'! This means that you should avoid using `-' on integers that may have the value of `-2^63'! `ABS(X)' Returns the absolute value of `X'. mysql> select ABS(2); -> 2 mysql> select ABS(-32); -> 32 This function is safe to use with `BIGINT' values. `SIGN(X)' Returns the sign of the argument as `-1', `0' or `1', depending on whether `X' is negative, zero, or positive. mysql> select SIGN(-32); -> -1 mysql> select SIGN(0); -> 0 mysql> select SIGN(234); -> 1 `MOD(N,M)' `%' Modulo (like the `%' operator in C). Returns the remainder of `N' divided by `M'. mysql> select MOD(234, 10); -> 4 mysql> select 253 % 7; -> 1 mysql> select MOD(29,9); -> 2 This function is safe to use with `BIGINT' values. `FLOOR(X)' Returns the largest integer value not greater than `X'. mysql> select FLOOR(1.23); -> 1 mysql> select FLOOR(-1.23); -> -2 Note that the return value is converted to a `BIGINT'! `CEILING(X)' Returns the smallest integer value not less than `X'. mysql> select CEILING(1.23); -> 2 mysql> select CEILING(-1.23); -> -1 Note that the return value is converted to a `BIGINT'! `ROUND(X)' Returns the argument `X', rounded to an integer. mysql> select ROUND(-1.23); -> -1 mysql> select ROUND(-1.58); -> -2 mysql> select ROUND(1.58); -> 2 Note that the return value is converted to a `BIGINT'! `ROUND(X,D)' Returns the argument `X', rounded to a number with `D' decimals. If `D' is `0', the result will have no decimal point or fractional part. mysql> select ROUND(1.298, 1); -> 1.3 mysql> select ROUND(1.298, 0); -> 1 Note that the return value is converted to a `BIGINT'! `EXP(X)' Returns the value of `e' (the base of natural logarithms) raised to the power of `X'. mysql> select EXP(2); -> 7.389056 mysql> select EXP(-2); -> 0.135335 `LOG(X)' Returns the natural logarithm of `X'. mysql> select LOG(2); -> 0.693147 mysql> select LOG(-2); -> NULL If you want the log of a number `X' to some arbitary base `B', use the formula `LOG(X)/LOG(B)'. `LOG10(X)' Returns the base-10 logarithm of `X'. mysql> select LOG10(2); -> 0.301030 mysql> select LOG10(100); -> 2.000000 mysql> select LOG10(-100); -> NULL `POW(X,Y)' `POWER(X,Y)' Returns the value of `X' raised to the power of `Y'. mysql> select POW(2,2); -> 4.000000 mysql> select POW(2,-2); -> 0.250000 `SQRT(X)' Returns the non-negative square root of `X'. mysql> select SQRT(4); -> 2.000000 mysql> select SQRT(20); -> 4.472136 `PI()' Returns the value of PI. mysql> select PI(); -> 3.141593 `COS(X)' Returns the cosine of `X', where `X' is given in radians. mysql> select COS(PI()); -> -1.000000 `SIN(X)' Returns the sine of `X', where `X' is given in radians. mysql> select SIN(PI()); -> 0.000000 `TAN(X)' Returns the tangent of `X', where `X' is given in radians. mysql> select TAN(PI()+1); -> 1.557408 `ACOS(X)' Returns the arc cosine of `X', that is, the value whose cosine is `X'. Returns `NULL' if `X' is not in the range `-1' to `1'. mysql> select ACOS(1); -> 0.000000 mysql> select ACOS(1.0001); -> NULL mysql> select ACOS(0); -> 1.570796 `ASIN(X)' Returns the arc sine of `X', that is, the value whose sine is `X'. Returns `NULL' if `X' is not in the range `-1' to `1'. mysql> select ASIN(0.2); -> 0.201358 mysql> select ASIN('foo'); -> 0.000000 `ATAN(X)' Returns the arc tangent of `X', that is, the value whose tangent is `X'. mysql> select ATAN(2); -> 1.107149 mysql> select ATAN(-2); -> -1.107149 `ATAN2(X,Y)' Returns the arc tangent of the two variables `X' and `Y'. It is similar to calculating the arc tangent of `Y / X', except that the signs of both arguments are used to determine the quadrant of the result. mysql> select ATAN(-2,2); -> -0.785398 mysql> select ATAN(PI(),0); -> 1.570796 `COT(X)' Returns the cotangent of `X'. mysql> select COT(12); -> -1.57267341 mysql> select COT(0); -> NULL `RAND()' `RAND(N)' Returns a random floating-point value in the range `0' to `1.0'. If an integer argument `N' is specified, it is used as the seed value. mysql> select RAND(); -> 0.5925 mysql> select RAND(20); -> 0.1811 mysql> select RAND(20); -> 0.1811 mysql> select RAND(); -> 0.2079 mysql> select RAND(); -> 0.7888 You can't use a column with `RAND()' values in an `ORDER BY' clause, because `ORDER BY' would evaluate the column multiple times. In *MySQL* 3.23, you can however do: `SELECT * FROM table_name ORDER BY RAND()' This is useful to get a random sample of a set `SELECT * FROM table1,table2 WHERE a=b AND c select LEAST(2,0); -> 0 mysql> select LEAST(34.0,3.0,5.0,767.0); -> 3.0 mysql> select LEAST("B","A","C"); -> "A" In *MySQL* versions prior to 3.22.5, you can use `MIN()' instead of `LEAST'. `GREATEST(X,Y,...)' Returns the largest (maximum-valued) argument. The arguments are compared using the same rules as for `LEAST'. mysql> select GREATEST(2,0); -> 2 mysql> select GREATEST(34.0,3.0,5.0,767.0); -> 767.0 mysql> select GREATEST("B","A","C"); -> "C" In *MySQL* versions prior to 3.22.5, you can use `MAX()' instead of `GREATEST'. `DEGREES(X)' Returns the argument `X', converted from radians to degrees. mysql> select DEGREES(PI()); -> 180.000000 `RADIANS(X)' Returns the argument `X', converted from degrees to radians. mysql> select RADIANS(90); -> 1.570796 `TRUNCATE(X,D)' Returns the number `X', truncated to `D' decimals. If `D' is `0', the result will have no decimal point or fractional part. mysql> select TRUNCATE(1.223,1); -> 1.2 mysql> select TRUNCATE(1.999,1); -> 1.9 mysql> select TRUNCATE(1.999,0); -> 1 String functions ---------------- String-valued functions return `NULL' if the length of the result would be greater than the `max_allowed_packet' server parameter. *Note Server parameters::. For functions that operate on string positions, the first position is numbered 1. `ASCII(str)' Returns the ASCII code value of the leftmost character of the string `str'. Returns `0' if `str' is the empty string. Returns `NULL' if `str' is `NULL'. mysql> select ASCII('2'); -> 50 mysql> select ASCII(2); -> 50 mysql> select ASCII('dx'); -> 100 `CONV(N,from_base,to_base)' Converts numbers between different number bases. Returns a string representation of the number `N', converted from base `from_base' to base `to_base'. Returns `NULL' if any argument is `NULL'. The argument `N' is interpreted as an integer, but may be specified as an integer or a string. The minimum base is `2' and the maximum base is `36'. If `to_base' is a negative number, `N' is regarded as a signed number. Otherwise, `N' is treated as unsigned. `CONV' works with 64-bit precision. mysql> select CONV("a",16,2); -> '1010' mysql> select CONV("6E",18,8); -> '172' mysql> select CONV(-17,10,-18); -> '-H' mysql> select CONV(10+"10"+'10'+0xa,10,10); -> '40' `BIN(N)' Returns a string representation of the binary value of `N', where `N' is a longlong (`BIGINT') number. This is equivalent to `CONV(N,10,2)'. Returns `NULL' if `N' is `NULL'. mysql> select BIN(12); -> '1100' `OCT(N)' Returns a string representation of the octal value of `N', where `N' is a longlong number. This is equivalent to `CONV(N,10,8)'. Returns `NULL' if `N' is `NULL'. mysql> select OCT(12); -> '14' `HEX(N)' Returns a string representation of the hexadecimal value of `N', where `N' is a longlong (`BIGINT') number. This is equivalent to `CONV(N,10,16)'. Returns `NULL' if `N' is `NULL'. mysql> select HEX(255); -> 'FF' `CHAR(N,...)' `CHAR()' interprets the arguments as integers and returns a string consisting of the characters given by the ASCII code values of those integers. `NULL' values are skipped. mysql> select CHAR(77,121,83,81,'76'); -> 'MySQL' mysql> select CHAR(77,77.3,'77.3'); -> 'MMM' `CONCAT(str1,str2,...)' Returns the string that results from concatenating the arguments. Returns `NULL' if any argument is `NULL'. May have more than 2 arguments. A numeric argument is converted to the equivalent string form. mysql> select CONCAT('My', 'S', 'QL'); -> 'MySQL' mysql> select CONCAT('My', NULL, 'QL'); -> NULL mysql> select CONCAT(14.3); -> '14.3' `LENGTH(str)' `OCTET_LENGTH(str)' `CHAR_LENGTH(str)' `CHARACTER_LENGTH(str)' Returns the length of the string `str'. mysql> select LENGTH('text'); -> 4 mysql> select OCTET_LENGTH('text'); -> 4 `LOCATE(substr,str)' `POSITION(substr IN str)' Returns the position of the first occurrence of substring `substr' in string `str'. Returns `0' if `substr' is not in `str'. mysql> select LOCATE('bar', 'foobarbar'); -> 4 mysql> select LOCATE('xbar', 'foobar'); -> 0 `LOCATE(substr,str,pos)' Returns the position of the first occurrence of substring `substr' in string `str', starting at position `pos'. Returns `0' if `substr' is not in `str'. mysql> select LOCATE('bar', 'foobarbar',5); -> 7 `INSTR(str,substr)' Returns the position of the first occurrence of substring `substr' in string `str'. This is the same as the two-argument form of `LOCATE()', except that the arguments are swapped. mysql> select INSTR('foobarbar', 'bar'); -> 4 mysql> select INSTR('xbar', 'foobar'); -> 0 `LPAD(str,len,padstr)' Returns the string `str', left-padded with the string `padstr' until `str' is `len' characters long. mysql> select LPAD('hi',4,'??'); -> '??hi' `RPAD(str,len,padstr)' Returns the string `str', right-padded with the string `padstr' until `str' is `len' characters long. mysql> select RPAD('hi',5,'?'); -> 'hi???' `LEFT(str,len)' Returns the leftmost `len' characters from the string `str'. mysql> select LEFT('foobarbar', 5); -> 'fooba' `RIGHT(str,len)' Returns the rightmost `len' characters from the string `str'. mysql> select RIGHT('foobarbar', 4); -> 'rbar' `SUBSTRING(str,pos,len)' `SUBSTRING(str FROM pos FOR len)' `MID(str,pos,len)' Returns a substring `len' characters long from string `str', starting at position `pos'. The variant form that uses `FROM' is ANSI SQL92 syntax. mysql> select SUBSTRING('Quadratically',5,6); -> 'ratica' `SUBSTRING(str,pos)' `SUBSTRING(str FROM pos)' Returns a substring from string `str' starting at position `pos'. mysql> select SUBSTRING('Quadratically',5); -> 'ratically' mysql> select SUBSTRING('foobarbar' FROM 4); -> 'barbar' `SUBSTRING_INDEX(str,delim,count)' Returns the substring from string `str' after `count' occurrences of the delimiter `delim'. If `count' is positive, everything to the left of the final delimiter (counting from the left) is returned. If `count' is negative, everything to the right of the final delimiter (counting from the right) is returned. mysql> select SUBSTRING_INDEX('www.mysql.com', '.', 2); -> 'www.mysql' mysql> select SUBSTRING_INDEX('www.mysql.com', '.', -2); -> 'mysql.com' `LTRIM(str)' Returns the string `str' with leading space characters removed. mysql> select LTRIM(' barbar'); -> 'barbar' `RTRIM(str)' Returns the string `str' with trailing space characters removed. mysql> select RTRIM('barbar '); -> 'barbar' `TRIM([[BOTH | LEADING | TRAILING] [remstr] FROM] str)' Returns the string `str' with all `remstr' prefixes and/or suffixes removed. If none of the specifiers `BOTH', `LEADING' or `TRAILING' are given, `BOTH' is assumed. If `remstr' is not specified, spaces are removed. mysql> select TRIM(' bar '); -> 'bar' mysql> select TRIM(LEADING 'x' FROM 'xxxbarxxx'); -> 'barxxx' mysql> select TRIM(BOTH 'x' FROM 'xxxbarxxx'); -> 'bar' mysql> select TRIM(TRAILING 'xyz' FROM 'barxxyz'); -> 'barx' `SOUNDEX(str)' Returns a soundex string from `str'. Two strings that sound "about the same" should have identical soundex strings. A "standard" soundex string is 4 characters long, but the `SOUNDEX()' function returns an arbitrarily long string. You can use `SUBSTRING()' on the result to get a "standard" soundex string. All non-alphanumeric characters are ignored in the given string. All international alpha characters outside the A-Z range are treated as vowels. mysql> select SOUNDEX('Hello'); -> 'H400' mysql> select SOUNDEX('Quadratically'); -> 'Q36324' `SPACE(N)' Returns a string consisting of `N' space characters. mysql> select SPACE(6); -> ' ' `REPLACE(str,from_str,to_str)' Returns the string `str' with all all occurrences of the string `from_str' replaced by the string `to_str'. mysql> select REPLACE('www.mysql.com', 'w', 'Ww'); -> 'WwWwWw.mysql.com' `REPEAT(str,count)' Returns a string consisting of the string `str' repeated `count' times. If `count <= 0', returns an empty string. Returns `NULL' if `str' or `count' are `NULL'. mysql> select REPEAT('MySQL', 3); -> 'MySQLMySQLMySQL' `REVERSE(str)' Returns the string `str' with the order of the characters reversed. mysql> select REVERSE('abc'); -> 'cba' `INSERT(str,pos,len,newstr)' Returns the string `str', with the substring beginning at position `pos' and `len' characters long replaced by the string `newstr'. mysql> select INSERT('Quadratic', 3, 4, 'What'); -> 'QuWhattic' `ELT(N,str1,str2,str3,...)' Returns `str1' if `N' = `1', `str2' if `N' = `2', and so on. Returns `NULL' if `N' is less than `1' or greater than the number of arguments. `ELT()' is the complement of `FIELD()'. mysql> select ELT(1, 'ej', 'Heja', 'hej', 'foo'); -> 'ej' mysql> select ELT(4, 'ej', 'Heja', 'hej', 'foo'); -> 'foo' `FIELD(str,str1,str2,str3,...)' Returns the index of `str' in the `str1', `str2', `str3', `...' list. Returns `0' if `str' is not found. `FIELD()' is the complement of `ELT()'. mysql> select FIELD('ej', 'Hej', 'ej', 'Heja', 'hej', 'foo'); -> 2 mysql> select FIELD('fo', 'Hej', 'ej', 'Heja', 'hej', 'foo'); -> 0 `FIND_IN_SET(str,strlist)' Returns a value `1' to `N' if the string `str' is in the list `strlist' consisting of `N' substrings. A string list is a string composed of substrings separated by `,' characters. If the first argument is a constant string and the second is a column of type `SET', the `FIND_IN_SET()' function is optimized to use bit arithmetic! Returns `0' if `str' is not in `strlist' or if `strlist' is the empty string. Returns `NULL' if either argument is `NULL'. This function will not work properly if the first argument contains a `,'. mysql> SELECT FIND_IN_SET('b','a,b,c,d'); -> 2 `MAKE_SET(bits,str1,str2,...)' Returns a set (a string containing substrings separated by `,' characters) consisting of the strings that have the corresponding bit in `bits' set. `str1' corresponds to bit 0, `str2' to bit 1, etc. `NULL' strings in `str1', `str2', `...' are not appended to the result. mysql> SELECT MAKE_SET(1,'a','b','c'); -> 'a' mysql> SELECT MAKE_SET(1 | 4,'hello','nice','world'); -> 'hello,world' mysql> SELECT MAKE_SET(0,'a','b','c'); -> '' `EXPORT_SET(bits,on,off,[separator,[number_of_bits]])' Returns a string where for every bit set in 'bit', you get a 'on' string and for every reset bit you get an 'off' string. Each string is separated with 'separator' (default ',') and only 'number_of_bits' (default 64) of 'bits' is used. mysql> select EXPORT_SET(5,'Y','N',',',4) -> Y,N,Y,N `LCASE(str)' `LOWER(str)' Returns the string `str' with all characters changed to lowercase according to the current character set mapping (the default is ISO-8859-1 Latin1). mysql> select LCASE('QUADRATICALLY'); -> 'quadratically' `UCASE(str)' `UPPER(str)' Returns the string `str' with all characters changed to uppercase according to the current character set mapping (the default is ISO-8859-1 Latin1). mysql> select UCASE('Hej'); -> 'HEJ' `LOAD_FILE(file_name)' Reads the file and returns the file contents as a string. The file must be on the server, you must specify the full pathname to the file, and you must have the *file* privilege. The file must be readable by all and be smaller than `max_allowed_packet'. If the file doesn't exist or can't be read due to one of the above reasons, the function returns `NULL'. mysql> UPDATE table_name SET blob_column=LOAD_FILE("/tmp/picture") WHERE id=1; *MySQL* automatically converts numbers to strings as necessary, and vice versa: mysql> SELECT 1+"1"; -> 2 mysql> SELECT CONCAT(2,' test'); -> '2 test' If you want to convert a number to a string explicitly, pass it as the argument to `CONCAT()'. If a string function is given a binary string as an argument, the resulting string is also a binary string. A number converted to a string is treated as a binary string. This only affects comparisons. Date and time functions ----------------------- See *Note Date and time types:: for a description of the range of values each type has, and the valid formats in which date and time values may be specified. Here is an example that uses date functions. The query below selects all records with a `date_col' value from within the last 30 days: mysql> SELECT something FROM table WHERE TO_DAYS(NOW()) - TO_DAYS(date_col) <= 30; `DAYOFWEEK(date)' Returns the weekday index for `date' (`1' = Sunday, `2' = Monday, ... `7' = Saturday). These index values correspond to the ODBC standard. mysql> select DAYOFWEEK('1998-02-03'); -> 3 `WEEKDAY(date)' Returns the weekday index for `date' (`0' = Monday, `1' = Tuesday, ... `6' = Sunday). mysql> select WEEKDAY('1997-10-04 22:23:00'); -> 5 mysql> select WEEKDAY('1997-11-05'); -> 2 `DAYOFMONTH(date)' Returns the day of the month for `date', in the range `1' to `31'. mysql> select DAYOFMONTH('1998-02-03'); -> 3 `DAYOFYEAR(date)' Returns the day of the year for `date', in the range `1' to `366'. mysql> select DAYOFYEAR('1998-02-03'); -> 34 `MONTH(date)' Returns the month for `date', in the range `1' to `12'. mysql> select MONTH('1998-02-03'); -> 2 `DAYNAME(date)' Returns the name of the weekday for `date'. mysql> select DAYNAME("1998-02-05"); -> 'Thursday' `MONTHNAME(date)' Returns the name of the month for `date'. mysql> select MONTHNAME("1998-02-05"); -> 'February' `QUARTER(date)' Returns the quarter of the year for `date', in the range `1' to `4'. mysql> select QUARTER('98-04-01'); -> 2 `WEEK(date)' `WEEK(date,first)' With a single argument, returns the week for `date', in the range `0' to `52', for locations where Sunday is the first day of the week. The two-argument form of `WEEK()' allows you to specify whether the week starts on Sunday or Monday. The week starts on Sunday if the second argument is `0', on Monday if the second argument is `1'. mysql> select WEEK('1998-02-20'); -> 7 mysql> select WEEK('1998-02-20',0); -> 7 mysql> select WEEK('1998-02-20',1); -> 8 `YEAR(date)' Returns the year for `date', in the range `1000' to `9999'. mysql> select YEAR('98-02-03'); -> 1998 `HOUR(time)' Returns the hour for `time', in the range `0' to `23'. mysql> select HOUR('10:05:03'); -> 10 `MINUTE(time)' Returns the minute for `time', in the range `0' to `59'. mysql> select MINUTE('98-02-03 10:05:03'); -> 5 `SECOND(time)' Returns the second for `time', in the range `0' to `59'. mysql> select SECOND('10:05:03'); -> 3 `PERIOD_ADD(P,N)' Adds `N' months to period `P' (in the format `YYMM' or `YYYYMM'). Returns a value in the format `YYYYMM'. Note that the period argument `P' is *not* a date value. mysql> select PERIOD_ADD(9801,2); -> 199803 `PERIOD_DIFF(P1,P2)' Returns the number of months between periods `P1' and `P2'. `P1' and `P2' should be in the format `YYMM' or `YYYYMM'. Note that the period arguments `P1' and `P2' are *not* date values. mysql> select PERIOD_DIFF(9802,199703); -> 11 `DATE_ADD(date,INTERVAL expr type)' `DATE_SUB(date,INTERVAL expr type)' `ADDDATE(date,INTERVAL expr type)' `SUBDATE(date,INTERVAL expr type)' These functions perform date arithmetic. They are new for *MySQL* 3.22. `ADDDATE()' and `SUBDATE()' are synonyms for `DATE_ADD()' and `DATE_SUB()'. In *MySQL* 3.23, you can use `+' and `-' instead of `DATE_ADD()' and `DATE_SUB()'. (See example) `date' is a `DATETIME' or `DATE' value specifying the starting date. `expr' is an expression specifying the interval value to be added or substracted from the starting date. `expr' is a string; it may start with a `-' for negative intervals. `type' is a keyword indicating how the expression should be interpreted. The `EXTRACT(type FROM date)' function returns the 'type' interval from the date. The following table shows how the `type' and `expr' arguments are related: `type' *Meaning* *Expected* `expr' *format* *value* `SECOND' Seconds `SECONDS' `MINUTE' Minutes `MINUTES' `HOUR' Hours `HOURS' `DAY' Days `DAYS' `MONTH' Months `MONTHS' `YEAR' Years `YEARS' `MINUTE_SECOND'Minutes and seconds `"MINUTES:SECONDS"' `HOUR_MINUTE'Hours and minutes `"HOURS:MINUTES"' `DAY_HOUR' Days and hours `"DAYS HOURS"' `YEAR_MONTH' Years and months `"YEARS-MONTHS"' `HOUR_SECOND'Hours, minutes, `"HOURS:MINUTES:SECONDS"' `DAY_MINUTE' Days, hours, `"DAYS HOURS:MINUTES"' minutes `DAY_SECOND' Days, hours, `"DAYS minutes, seconds HOURS:MINUTES:SECONDS"' *MySQL* allows any punctuation delimiter in the `expr' format. The ones shown in the table are the suggested delimiters. If the `date' argument is a `DATE' value and your calculations involve only `YEAR', `MONTH' and `DAY' parts (that is, no time parts), the result is a `DATE' value. Otherwise the result is a `DATETIME' value. mysql> SELECT "1997-12-31 23:59:59" + INTERVAL 1 SECOND; -> 1998-01-01 00:00:00 mysql> SELECT INTERVAL 1 DAY + "1997-12-31"; -> 1998-01-01 mysql> SELECT "1998-01-01" - INTERVAL 1 SECOND; -> 1997-12-31 23:59:59 mysql> SELECT DATE_ADD("1997-12-31 23:59:59", INTERVAL 1 SECOND); -> 1998-01-01 00:00:00 mysql> SELECT DATE_ADD("1997-12-31 23:59:59", INTERVAL 1 DAY); -> 1998-01-01 23:59:59 mysql> SELECT DATE_ADD("1997-12-31 23:59:59", INTERVAL "1:1" MINUTE_SECOND); -> 1998-01-01 00:01:00 mysql> SELECT DATE_SUB("1998-01-01 00:00:00", INTERVAL "1 1:1:1" DAY_SECOND); -> 1997-12-30 22:58:59 mysql> SELECT DATE_ADD("1998-01-01 00:00:00", INTERVAL "-1 10" DAY_HOUR); -> 1997-12-30 14:00:00 mysql> SELECT DATE_SUB("1998-01-02", INTERVAL 31 DAY); -> 1997-12-02 mysql> SELECT EXTRACT(YEAR FROM "1999-07-02"); -> 1999 mysql> SELECT EXTRACT(YEAR_MONTH FROM "1999-07-02 01:02:03"); -> 199907 mysql> SELECT EXTRACT(DAY_MINUTE FROM "1999-07-02 01:02:03"); -> 20102 If you specify an interval value that is too short (does not include all the interval parts that would be expected from the `type' keyword), *MySQL* assumes you have left out the leftmost parts of the interval value. For example, if you specify a `type' of `DAY_SECOND', the value of `expr' is expected to have days, hours, minutes and seconds parts. If you specify a value like `"1:10"', *MySQL* assumes that the days and hours parts are missing and the value represents minutes and seconds. In other words, `"1:10" DAY_SECOND' is interpreted in such a way that it is equivalent to `"1:10" MINUTE_SECOND'. This is analogous to the way that *MySQL* interprets `TIME' values as representing elapsed time rather than as time of day. If you use incorrect dates, the result is `NULL'. If you add `MONTH', `YEAR_MONTH' or `YEAR' and the resulting date has a day that is larger than the maximum day for the new month, the day is adjusted to the maximum days in the new month. mysql> select DATE_ADD('1998-01-30', Interval 1 month); -> 1998-02-28 Note from the preceding example that the word `INTERVAL' and the `type' keyword are not case sensitive. `TO_DAYS(date)' Given a date `date', returns a daynumber (the number of days since year 0). mysql> select TO_DAYS(950501); -> 728779 mysql> select TO_DAYS('1997-10-07'); -> 729669 `TO_DAYS()' is not intended for use with values that precede the advent of the Gregorian calendar (1582). `FROM_DAYS(N)' Given a daynumber `N', returns a `DATE' value. mysql> select FROM_DAYS(729669); -> '1997-10-07' `FROM_DAYS()' is not intended for use with values that precede the advent of the Gregorian calendar (1582). `DATE_FORMAT(date,format)' Formats the `date' value according to the `format' string. The following specifiers may be used in the `format' string: `%M' Month name (`January'..`December') `%W' Weekday name (`Sunday'..`Saturday') `%D' Day of the month with english suffix (`1st', `2nd', `3rd', etc.) `%Y' Year, numeric, 4 digits `%y' Year, numeric, 2 digits `%a' Abbreviated weekday name (`Sun'..`Sat') `%d' Day of the month, numeric (`00'..`31') `%e' Day of the month, numeric (`0'..`31') `%m' Month, numeric (`01'..`12') `%c' Month, numeric (`1'..`12') `%b' Abbreviated month name (`Jan'..`Dec') `%j' Day of year (`001'..`366') `%H' Hour (`00'..`23') `%k' Hour (`0'..`23') `%h' Hour (`01'..`12') `%I' Hour (`01'..`12') `%l' Hour (`1'..`12') `%i' Minutes, numeric (`00'..`59') `%r' Time, 12-hour (`hh:mm:ss [AP]M') `%T' Time, 24-hour (`hh:mm:ss') `%S' Seconds (`00'..`59') `%s' Seconds (`00'..`59') `%p' `AM' or `PM' `%w' Day of the week (`0'=Sunday..`6'=Saturday) `%U' Week (`0'..`52'), where Sunday is the first day of the week `%u' Week (`0'..`52'), where Monday is the first day of the week `%%' A literal `%'. All other characters are just copied to the result without interpretation. mysql> select DATE_FORMAT('1997-10-04 22:23:00', '%W %M %Y'); -> 'Saturday October 1997' mysql> select DATE_FORMAT('1997-10-04 22:23:00', '%H:%i:%s'); -> '22:23:00' mysql> select DATE_FORMAT('1997-10-04 22:23:00', '%D %y %a %d %m %b %j'); -> '4th 97 Sat 04 10 Oct 277' mysql> select DATE_FORMAT('1997-10-04 22:23:00', '%H %k %I %r %T %S %w'); -> '22 22 10 10:23:00 PM 22:23:00 00 6' As of *MySQL* 3.23, the `%' is required before a format specifier characters. In earlier versions of *MySQL*, `%' was optional. `TIME_FORMAT(time,format)' This is used like the `DATE_FORMAT()' function above, but the `format' string may contain only those format specifiers that handle hours, minutes and seconds. Other specifiers produce a `NULL' value or `0'. `CURDATE()' `CURRENT_DATE' Returns today's date as a value in `'YYYY-MM-DD'' or `YYYYMMDD' format, depending on whether the function is used in a string or numeric context. mysql> select CURDATE(); -> '1997-12-15' mysql> select CURDATE() + 0; -> 19971215 `CURTIME()' `CURRENT_TIME' Returns the current time as a value in `'HH:MM:SS'' or `HHMMSS' format, depending on whether the function is used in a string or numeric context. mysql> select CURTIME(); -> '23:50:26' mysql> select CURTIME() + 0; -> 235026 `NOW()' `SYSDATE()' `CURRENT_TIMESTAMP' Returns the current date and time as a value in `'YYYY-MM-DD HH:MM:SS'' or `YYYYMMDDHHMMSS' format, depending on whether the function is used in a string or numeric context. mysql> select NOW(); -> '1997-12-15 23:50:26' mysql> select NOW() + 0; -> 19971215235026 `UNIX_TIMESTAMP()' `UNIX_TIMESTAMP(date)' If called with no argument, returns a Unix timestamp (seconds since `'1970-01-01 00:00:00'' GMT). If `UNIX_TIMESTAMP()' is called with a `date' argument, it returns the value of the argument as seconds since `'1970-01-01 00:00:00'' GMT. `date' may be a `DATE' string, a `DATETIME' string, a `TIMESTAMP', or a number in the format `YYMMDD' or `YYYYMMDD' in local time. mysql> select UNIX_TIMESTAMP(); -> 882226357 mysql> select UNIX_TIMESTAMP('1997-10-04 22:23:00'); -> 875996580 When `UNIX_TIMESTAMP' is used on a `TIMESTAMP' column, the function will receive the value directly, with no implicit "string-to-unix-timestamp" conversion. `FROM_UNIXTIME(unix_timestamp)' Returns a representation of the `unix_timestamp' argument as a value in `'YYYY-MM-DD HH:MM:SS'' or `YYYYMMDDHHMMSS' format, depending on whether the function is used in a string or numeric context. mysql> select FROM_UNIXTIME(875996580); -> '1997-10-04 22:23:00' mysql> select FROM_UNIXTIME(875996580) + 0; -> 19971004222300 `FROM_UNIXTIME(unix_timestamp,format)' Returns a string representation of the Unix timestamp, formatted according to the `format' string. `format' may contain the same specifiers as those listed in the entry for the `DATE_FORMAT()' function. mysql> select FROM_UNIXTIME(UNIX_TIMESTAMP(), '%Y %D %M %h:%i:%s %x'); -> '1997 23rd December 03:43:30 x' `SEC_TO_TIME(seconds)' Returns the `seconds' argument, converted to hours, minutes and seconds, as a value in `'HH:MM:SS'' or `HHMMSS' format, depending on whether the function is used in a string or numeric context. mysql> select SEC_TO_TIME(2378); -> '00:39:38' mysql> select SEC_TO_TIME(2378) + 0; -> 3938 `TIME_TO_SEC(time)' Returns the `time' argument, converted to seconds. mysql> select TIME_TO_SEC('22:23:00'); -> 80580 mysql> select TIME_TO_SEC('00:39:38'); -> 2378 Miscellaneous functions ----------------------- `DATABASE()' Returns the current database name. mysql> select DATABASE(); -> 'test' If there is no current database, `DATABASE()' returns the empty string. `USER()' `SYSTEM_USER()' `SESSION_USER()' Returns the current *MySQL* user name. mysql> select USER(); -> 'davida@localhost' In MySQL 3.22.11 or later, this includes the client hostname as well as the username. You can extract just the username part like this (which works whether or not the value includes a hostname part): mysql> select substring_index(USER(),"@",1); -> 'davida' `PASSWORD(str)' Calculates a password string from the plaintext password `str'. This is the function that is used for encrypting *MySQL* passwords for storage in the `Password' column of the `user' grant table. mysql> select PASSWORD('badpwd'); -> '7f84554057dd964b' `PASSWORD()' encryption is non-reversible. `PASSWORD()' does not perform password encryption in the same way that Unix passwords are encrypted. You should not assume that if your Unix password and your *MySQL* password are the same, `PASSWORD()' will result in the same encrypted value as is stored in the Unix password file. See `ENCRYPT()'. `ENCRYPT(str[,salt])' Encrypt `str' using the Unix `crypt()' system call. The `salt' argument should be a string with two characters. (As of MySQL 3.22.16, `salt' may be longer than two characters.) mysql> select ENCRYPT("hello"); -> 'VxuFAJXVARROc' If `crypt()' is not available on your system, `ENCRYPT()' always returns `NULL'. `ENCRYPT()' ignores all but the first 8 characters of `str', at least on some systems. This will be determined by the behavior of the underlying `crypt()' system call. `ENCODE(str,pass_str)' Encrypt `str' using `pass_str' as the password. To decrypt the result, use `DECODE()'. The results is a binary string. If you want to save it in a column, use a `BLOB' column type. `DECODE(crypt_str,pass_str)' Descrypts the encrypted string `crypt_str' using `pass_str' as the password. `crypt_str' should be a string returned from `ENCODE()'. `MD5(string)' Calculates a MD5 checksum for the string. Value is returned as a 32 long hex number that may, for example, be used as a hash key. mysql> select MD5("testing") -> 'ae2b1fca515949e5d54fb22b8ed95575' This is a "RSA Data Security, Inc. MD5 Message-Digest Algorithm". `LAST_INSERT_ID([expr])' Returns the last automatically generated value that was inserted into an `AUTO_INCREMENT' column. *Note `mysql_insert_id()': mysql_insert_id. mysql> select LAST_INSERT_ID(); -> 195 The last ID that was generated is maintained in the server on a per-connection basis. It will not be changed by another client. It will not even be changed if you update another `AUTO_INCREMENT' column with a non-magic value (that is, a value that is not `NULL' and not `0'). If `expr' is given as an argument to `LAST_INSERT_ID()' in an `UPDATE' clause, then the value of the argument is returned as a `LAST_INSERT_ID()' value. This can be used to simulate sequences: First create the table: mysql> create table sequence (id int not null); mysql> insert into sequence values (0); Then the table can be used to generate sequence numbers like this: mysql> update sequence set id=LAST_INSERT_ID(id+1); You can generate sequences without calling `LAST_INSERT_ID()', but the utility of using the function this way is that the ID value is maintained in the server as the last automatically generated value. You can retrieve the new ID as you would read any normal `AUTO_INCREMENT' value in *MySQL*. For example, `LAST_INSERT_ID()' (without an argument) will return the new ID. The C API function `mysql_insert_id()' can also be used to get the value. `FORMAT(X,D)' Formats the number `X' to a format like `'#,###,###.##'', rounded to `D' decimals. If `D' is `0', the result will have no decimal point or fractional part. mysql> select FORMAT(12332.123456, 4); -> '12,332.1235' mysql> select FORMAT(12332.1,4); -> '12,332.1000' mysql> select FORMAT(12332.2,0); -> '12,332' `VERSION()' Returns a string indicating the *MySQL* server version. mysql> select VERSION(); -> '3.22.19b-log' `GET_LOCK(str,timeout)' Tries to obtain a lock with a name given by the string `str', with a timeout of `timeout' seconds. Returns `1' if the lock was obtained successfully, `0' if the attempt timed out, or `NULL' if an error occurred (such as running out of memory or the thread was killed with `mysqladmin kill'). A lock is released when you execute `RELEASE_LOCK()', execute a new `GET_LOCK()' or the thread terminates. This function can be used to implement application locks or to simulate record locks. It blocks requests by other clients for locks with the same name; clients that agree on a given lock string name can use the string to perform cooperative advisory locking. mysql> select GET_LOCK("lock1",10); -> 1 mysql> select GET_LOCK("lock2",10); -> 1 mysql> select RELEASE_LOCK("lock2"); -> 1 mysql> select RELEASE_LOCK("lock1"); -> NULL Note that the second `RELEASE_LOCK()' call returns `NULL' because the lock `"lock1"' was automatically released by the second `GET_LOCK()' call. `RELEASE_LOCK(str)' Releases the lock named by the string `str' that was obtained with `GET_LOCK()'. Returns `1' if the lock was released, `0' if the lock wasn't locked by this thread (in which case the lock is not released) and `NULL' if the named lock didn't exist. The lock will not exist if it was never obtained by a call to `GET_LOCK()' or if it already has been released. `BENCHMARK(count,expr)' The `BENCHMARK()' function executes the expression `expr' repeatedly `count' times. It may be used to time how fast *MySQL* processes the expression. The result value is always `0'. The intended use is in the `mysql' client, which reports query execution times. mysql> select BENCHMARK(1000000,encode("hello","goodbye")); +----------------------------------------------+ | BENCHMARK(1000000,encode("hello","goodbye")) | +----------------------------------------------+ | 0 | +----------------------------------------------+ 1 row in set (4.74 sec) The time reported is elapsed time on the client end, not CPU time on the server end. It may be advisable to execute `BENCHMARK()' several times, and interpret the result with regard to how heavily loaded the server machine is. Functions for use with `GROUP BY' clauses ----------------------------------------- If you use a group function in a statement containing no `GROUP BY' clause, it is equivalent to grouping on all rows. `COUNT(expr)' Returns a count of the number of non-`NULL' values in the rows retrieved by a `SELECT' statement. mysql> select student.student_name,COUNT(*) from student,course where student.student_id=course.student_id GROUP BY student_name; `COUNT(*)' is somewhat different in that it returns a count of the number of rows retrieved, whether or not they contain `NULL' values. `COUNT(*)' is optimized to return very quickly if the `SELECT' retrieves from one table, no other columns are retrieved and there is no `WHERE' clause. For example: mysql> select COUNT(*) from student; `COUNT(DISTINCT expr,[expr...])' Returns a count of the number of different values. mysql> select COUNT(DISTINCT results) from student; In *MySQL* you can get the number of distinct expressions combinations by giving a list of expressions. In ANSI SQL you would have to do a concatenation of all expressions inside `CODE(DISTINCT ..)'. `AVG(expr)' Returns the average value of `expr'. mysql> select student_name, AVG(test_score) from student GROUP BY student_name; `MIN(expr)' `MAX(expr)' Returns the minimum or maximum value of `expr'. `MIN()' and `MAX()' may take a string argument; in such cases they return the minimum or maximum string value. mysql> select student_name, MIN(test_score), MAX(test_score) from student GROUP BY student_name; `SUM(expr)' Returns the sum of `expr'. Note that if the return set has no rows, it returns NULL! `STD(expr)' `STDDEV(expr)' Returns the standard deviation of `expr'. This is an extension to ANSI SQL. The `STDDEV()' form of this function is provided for Oracle compatability. `BIT_OR(expr)' Returns the bitwise `OR' of all bits in `expr'. The calculation is performed with 64-bit (`BIGINT' precision. `BIT_AND(expr)' Returns the bitwise `AND' of all bits in `expr'. The calculation is performed with 64-bit (`BIGINT' precision. *MySQL* has extended the use of `GROUP BY'. You can use columns or calculations in the `SELECT' expressions which don't appear in the `GROUP BY' part. This stands for *any possible value for this group*. You can use this to get better performance by avoiding sorting and grouping on unnecessary items. For example, you don't need to group on `customer.name' in the following query: mysql> select order.custid,customer.name,max(payments) from order,customer where order.custid = customer.custid GROUP BY order.custid; In ANSI SQL, you would have to add `customer.name' to the `GROUP BY' clause. In *MySQL*, the name is redundant. Don't use this feature if the columns you omit from the `GROUP BY' part aren't unique in the group! In some cases, you can use `MIN()' and `MAX()' to obtain a specific column value even if it isn't unique. The following gives the value of `column' from the row containing the smallest value in the `sort' column: substr(MIN(concat(sort,space(6-length(sort)),column),7,length(column))) Note that if you are using *MySQL* 3.22 (or earlier) or if you are trying to follow ANSI SQL, you can't use expressions in `GROUP BY' or `ORDER BY' clauses. You can work around this limitation by using an alias for the expression: mysql> SELECT id,FLOOR(value/100) AS val FROM tbl_name GROUP BY id,val ORDER BY val; In `MySQL' 3.23 you can do: mysql> SELECT id,FLOOR(value/100) FROM tbl_name ORDER BY RAND(); `CREATE DATABASE' syntax ======================== CREATE DATABASE db_name `CREATE DATABASE' creates a database with the given name. Rules for allowable database names are given in *Note Legal names::. An error occurs if the database already exists. Databases in *MySQL* are implemented as directories containing files that correspond to tables in the database. Since there are no tables in a database when it is initially created, the `CREATE DATABASE' statement only creates a directory under the *MySQL* data directory. You can also create databases with `mysqladmin'. *Note Programs::. `DROP DATABASE' syntax ====================== DROP DATABASE [IF EXISTS] db_name `DROP DATABASE' drops all tables in the database and deletes the database. *Be VERY careful with this command!* `DROP DATABASE' returns the number of files that were removed from the database directory. Normally, this is three times the number of tables, since each table corresponds to a `.ISD' file, a `.ISM' file and a `.frm' file. In *MySQL* 3.22 or later, you can use the keywords `IF EXISTS' to prevent an error from occurring if the database doesn't exist. You can also drop databases with `mysqladmin'. *Note Programs::. `CREATE TABLE' syntax ===================== CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name (create_definition,...) [table_options] [select_statement] create_definition: col_name type [NOT NULL | NULL] [DEFAULT default_value] [AUTO_INCREMENT] [PRIMARY KEY] [reference_definition] or PRIMARY KEY (index_col_name,...) or KEY [index_name] (index_col_name,...) or INDEX [index_name] (index_col_name,...) or UNIQUE [INDEX] [index_name] (index_col_name,...) or [CONSTRAINT symbol] FOREIGN KEY index_name (index_col_name,...) [reference_definition] or CHECK (expr) type: TINYINT[(length)] [UNSIGNED] [ZEROFILL] or SMALLINT[(length)] [UNSIGNED] [ZEROFILL] or MEDIUMINT[(length)] [UNSIGNED] [ZEROFILL] or INT[(length)] [UNSIGNED] [ZEROFILL] or INTEGER[(length)] [UNSIGNED] [ZEROFILL] or BIGINT[(length)] [UNSIGNED] [ZEROFILL] or REAL[(length,decimals)] [UNSIGNED] [ZEROFILL] or DOUBLE[(length,decimals)] [UNSIGNED] [ZEROFILL] or FLOAT[(length,decimals)] [UNSIGNED] [ZEROFILL] or DECIMAL(length,decimals) [UNSIGNED] [ZEROFILL] or NUMERIC(length,decimals) [UNSIGNED] [ZEROFILL] or CHAR(length) [BINARY] or VARCHAR(length) [BINARY] or DATE or TIME or TIMESTAMP or DATETIME or TINYBLOB or BLOB or MEDIUMBLOB or LONGBLOB or TINYTEXT or TEXT or MEDIUMTEXT or LONGTEXT or ENUM(value1,value2,value3,...) or SET(value1,value2,value3,...) index_col_name: col_name [(length)] reference_definition: REFERENCES tbl_name [(index_col_name,...)] [MATCH FULL | MATCH PARTIAL] [ON DELETE reference_option] [ON UPDATE reference_option] reference_option: RESTRICT | CASCADE | SET NULL | NO ACTION | SET DEFAULT table_options: TYPE = {ISAM | MYISAM | HEAP} or AUTO_INCREMENT = # or AVG_ROW_LENGTH = # or CHECKSUM = {0 | 1} or COMMENT = "string" or MAX_ROWS = # or MIN_ROWS = # or PACK_KEYS = {0 | 1} or PASSWORD = "string" or DELAY_KEY_WRITE = {0 | 1} select_statement: [IGNORE | REPLACE] SELECT ... (Some legal select statement) `CREATE TABLE' creates a table with the given name in the current database. Rules for allowable table names are given in *Note Legal names::. An error occurs if there is no current database or if the table already exists. In *MySQL* 3.22 or later, the table name can be specified as `db_name.tbl_name'. This works whether or not there is a current database. In *MySQL* 3.23, you can use the `TEMPORARY' keyword when you create a table. A temporary table will automatically be deleted if a connection dies and the name is per connection. This means that two different connections can both use the same temporary table name without conflicting with each other or with an existing table of the same name. (The existing table is hidden until the temporary table is deleted). In *MySQL* 3.23 or later, you can use the keywords `IF NOT EXISTS' so that an error does not occur if the table already exists. Note that there is no verification that the table structures are identical. Each table `tbl_name' is represented by some files in the database directory. In the case of ISAM-type tables you will get: *File* *Purpose* `tbl_name.frm' Table definition (form) file `tbl_name.ISD' Data file `tbl_name.ISM' Index file For more information on the properties of the various column types, see *Note Column types::. * If neither `NULL' nor `NOT NULL' is specified, the column is treated as though `NULL' had been specified. * An integer column may have the additional attribute `AUTO_INCREMENT'. When you insert a value of `NULL' (recommended) or `0' into an `AUTO_INCREMENT' column, the column is set to `value+1', where `value' is the largest value for the column currently in the table. `AUTO_INCREMENT' sequences begin with `1'. *Note `mysql_insert_id()': mysql_insert_id. If you delete the row containing the maximum value for an `AUTO_INCREMENT' column, the value will be reused. If you delete all rows in the table, the sequence starts over. *Note:* There can be only one `AUTO_INCREMENT' column per table, and it must be indexed. To make *MySQL* compatible with some ODBC applications, you can find the last inserted row with the following query: SELECT * FROM tbl_name WHERE auto_col IS NULL * `NULL' values are handled differently for `TIMESTAMP' columns than for other column types. You cannot store a literal `NULL' in a `TIMESTAMP' column; setting the column to `NULL' sets it to the current date and time. Because `TIMESTAMP' columns behave this way, the `NULL' and `NOT NULL' attributes do not apply in the normal way and are ignored if you specify them. On the other hand, to make it easier for *MySQL* clients to use `TIMESTAMP' columns, the server reports that such columns may be assigned `NULL' values (which is true), even though `TIMESTAMP' never actually will contain a `NULL' value. You can see this when you use `DESCRIBE tbl_name' to get a description of your table. Note that setting a `TIMESTAMP' column to `0' is not the same as setting it to `NULL', because `0' is a valid `TIMESTAMP' value. * If no `DEFAULT' value is specified for a column, *MySQL* automatically assigns one. If the column may take `NULL' as a value, the default value is `NULL'. If the column is declared as `NOT NULL', the default value depends on the column type: - For numeric types other than those declared with the `AUTO_INCREMENT' attribute, the default is `0'. For an `AUTO_INCREMENT' column, the default value is the next value in the sequence. - For date and time types other than `TIMESTAMP', the default is the appropriate "zero" value for the type. For the first `TIMESTAMP' column in a table, the default value is the current date and time. *Note Date and time types::. - For string types other than `ENUM', the default is the empty string. For `ENUM', the default is the first enumeration value. * `KEY' is a synonym for `INDEX'. * In *MySQL*, a `UNIQUE' key can have only distinct values. An error occurs if you try to add a new row with a key that matches an existing row. * In *MySQL* a `PRIMARY KEY' is the same thing as a unique `KEY' that is named `PRIMARY'. A table can have only one `PRIMARY KEY'. If you don't have a `PRIMARY KEY' and some applications ask for the `PRIMARY KEY' in your tables, *MySQL* will return the first `UNIQUE' key as the `PRIMARY KEY'. * A `PRIMARY KEY' can be a multiple-column index. However, you cannot create a multiple-column index using the `PRIMARY KEY' key attibute in a column specification. Doing so will mark only that single column as primary. You must use the `PRIMARY KEY(index_col_name, ...)' syntax. * If you don't assign a name to an index, the index will be assigned the same name as the first `index_col_name', with an optional suffix (`_2', `_3', `...') to make it unique. You can see index names for a table using `SHOW INDEX FROM tbl_name'. *Note `SHOW': SHOW. * Only the `MyISAM' table type supports indexes on columns that can have `NULL' values. In other cases you must declare such columns `NOT NULL' or an error results. * With `col_name(length)' syntax, you can specify an index which uses only a part of a `CHAR' or `VARCHAR' column. This can make the index file much smaller. *Note Indexes::. * Only the `MyISAM' table type supports indexing on `BLOB' and `TEXT' columns. When putting an index on a `BLOB' or `TEXT' column you MUST always specify the length of the index: CREATE TABLE test (blob_col BLOB, index(blob_col(10))); * When you use `ORDER BY' or `GROUP BY' with a `TEXT' or `BLOB' column, only the first `max_sort_length' bytes are used. *Note `BLOB': BLOB. * The `FOREIGN KEY', `CHECK' and `REFERENCES' clauses don't actually do anything. The syntax for them is provided only for compatibility, to make it easier to port code from other SQL servers and to run applications that create tables with references. *Note Missing functions::. * Each `NULL' column takes one bit extra, rounded up to the nearest byte. * The maximum record length in bytes can be calculated as follows: row length = 1 + (sum of column lengths) + (number of NULL columns + 7)/8 + (number of variable-length columns) * The `table_options' and `SELECT' options is only implemented in *MySQL* 3.23 and above. The different table types are: ISAM The original table handler MyISAM The new binary portable table handler HEAP The data for this table is only stored in memory *Note Table types::. The other table options are used to optimize the behavior of the table. In most cases, you don't have to specify any of them. The options work for all table types, if not otherwise indicated. `AUTO_INCREMENT'The next auto_increment value you want to set for your table (MyISAM) `AVG_ROW_LENGTH'An approximation of the average row length for your table. You only need to set this for tables with variable size records. `CHECKSUM' Set this to 1 if you want *MySQL* to maintain a checksum for all rows (makes the table a little slower to update but makes it easier to find corrupted tables) (MyISAM) `COMMENT' A 60 character comment for your table `MAX_ROWS' Max number of rows you plan to store in the table `MIN_ROWS' Minimum number of rows you plan to store in the table `PACK_KEYS' Set this to 1 if you want to have smaller index. This usually makes updates slower and reads faster (MyISAM, ISAM). `PASSWORD' Encrypt the `.frm' file with a password. This option doesn't do anything in the standard *MySQL* version. `DELAY_KEY_WRITE'Set this to 1 if want to delay key table updates until the table is closed (MyISAM). When you use a `MyISAM' table, *MySQL* uses the product of `max_rows * avg_row_length' to decide how big the resulting table will be. If you don't specify any of the above options, the maximum size for a table will be 4G (or 2G if your operating systems only supports 2G tables). * If you specify a `SELECT' after the `CREATE STATEMENT', *MySQL* will create new fields for all elements in the `SELECT'. For example: mysql> CREATE TABLE test (a int not null auto_increment, primary key (a), key(b)) TYPE=HEAP SELECT b,c from test2; This will create a `HEAP' table with 3 columns. Note that the table will automatically be deleted if any errors occur while copying data into the table. Silent column specification changes ----------------------------------- In some cases, *MySQL* silently changes a column specification from that given in a `CREATE TABLE' statement. (This may also occur with `ALTER TABLE'.) * `VARCHAR' columns with a length less than four are changed to `CHAR'. * If any column in a table has a variable length, the entire row is variable-length as a result. Therefore, if a table contains any variable-length columns (`VARCHAR', `TEXT' or `BLOB'), all `CHAR' columns longer than three characters are changed to `VARCHAR' columnss. This doesn't affect how you use the columns in any way; in *MySQL*, `VARCHAR' is just a different way to store characters. *MySQL* performs this conversion because it saves space and makes table operations faster. *Note Row format::. * `TIMESTAMP' display sizes must be even and in the range from 2 to 14. If you specify a display size of 0 or greater than 14, the size is coerced to 14. Odd-valued sizes in the range from 1 to 13 are coerced to the next higher even number. * You cannot store a literal `NULL' in a `TIMESTAMP' column; setting it to `NULL' sets it to the current date and time. Because `TIMESTAMP' columns behave this way, the `NULL' and `NOT NULL' attributes do not apply in the normal way and are ignored if you specify them. `DESCRIBE tbl_name' always reports that a `TIMESTAMP' column may be assigned `NULL' values. * *MySQL* maps certain column types used by other SQL database vendors to *MySQL* types. *Note Other-vendor column types::. If you want to see whether or not *MySQL* used a column type other than the one you specified, issue a `DESCRIBE tbl_name' statement after creating or altering your table. Certain other column type changes may occur if you compress a table using `pack_isam'. *Note Row format::. `ALTER TABLE' syntax ==================== ALTER [IGNORE] TABLE tbl_name alter_spec [, alter_spec ...] alter_specification: ADD [COLUMN] create_definition [FIRST | AFTER column_name ] or ADD INDEX [index_name] (index_col_name,...) or ADD PRIMARY KEY (index_col_name,...) or ADD UNIQUE [index_name] (index_col_name,...) or ALTER [COLUMN] col_name {SET DEFAULT literal | DROP DEFAULT} or CHANGE [COLUMN] old_col_name create_definition or MODIFY [COLUMN] create_definition or DROP [COLUMN] col_name or DROP PRIMARY KEY or DROP INDEX index_name or RENAME [AS] new_tbl_name or table_options `ALTER TABLE' allows you to change the structure of an existing table. For example, you can add or delete columns, create or destroy indexes, change the type of existing columns, or rename columns or the table itself. You can also change the comment for the table and type of the table. *Note `CREATE TABLE': CREATE TABLE. If you use `ALTER TABLE' to change a column specification but `DESCRIBE tbl_name' indicates that your column was not changed, it is possible that *MySQL* ignored your modification for one of the reasons described in *Note Silent column changes::. For example, if you try to change a `VARCHAR' column to `CHAR', *MySQL* will still use `VARCHAR' if the table contains other variable-length columns. `ALTER TABLE' works by making a temporary copy of the original table. The alteration is performed on the copy, then the original table is deleted and the new one is renamed. This is done in such a way that all updates are automatically redirected to the new table without any failed updates. While `ALTER TABLE' is executing, the original table is readable by other clients. Updates and writes to the table are stalled until the new table is ready. * To use `ALTER TABLE', you need *select*, *insert*, *delete*, *update*, *create* and *drop* privileges on the table. * `IGNORE' is a *MySQL* extension to ANSI SQL92. It controls how `ALTER TABLE' works if there are duplicates on unique keys in the new table. If `IGNORE' isn't specified, the copy is aborted and rolled back. If `IGNORE' is specified, then for rows with duplicates on a unique key, only the first row is used; the others are deleted. * You can issue multiple `ADD', `ALTER', `DROP' and `CHANGE' clauses in a single `ALTER TABLE' statement. This is a *MySQL* extension to ANSI SQL92, which allows only one of each clause per `ALTER TABLE' statement. * `CHANGE col_name', `DROP col_name' and `DROP INDEX' are *MySQL* extensions to ANSI SQL92. * `MODIFY' is an Oracle extension to `ALTER TABLE'. * The optional word `COLUMN' is a pure noise word and can be omitted. * If you use `ALTER TABLE tbl_name RENAME AS new_name' without any other options, *MySQL* simply renames the files that correspond to the table `tbl_name'. There is no need to create the temporary table. * `create_definition' clauses use the same syntax for `ADD' and `CHANGE' as for `CREATE TABLE'. Note that this syntax includes the column name, not just the column type. *Note `CREATE TABLE': CREATE TABLE. * You can rename a column using a `CHANGE old_col_name create_definition' clause. To do so, specify the old and new column names and the type that the column currently has. For example, to rename an `INTEGER' column from `a' to `b', you can do this: mysql> ALTER TABLE t1 CHANGE a b INTEGER; If you want to change a column's type but not the name, `CHANGE' syntax still requires two column names even if they are the same. For example: mysql> ALTER TABLE t1 CHANGE b b BIGINT NOT NULL; However, as of *MySQL* 3.22.16a, you can also use `MODIFY' to change a column's type without renaming it: mysql> ALTER TABLE t1 MODIFY b BIGINT NOT NULL; * If you use `CHANGE' or `MODIFY' to shorten a column for which an index exists on part of the column (for instance, if you have an index on the first 10 characters of a `VARCHAR' column), you cannot make the column shorter than the number of characters that are indexed. * When you change a column type using `CHANGE' or `MODIFY', *MySQL* tries to convert data to the new type as well as possible. * In *MySQL* 3.22 or later, you can use `FIRST' or `ADD ... AFTER col_name' to add a column at a specific position within a table row. The default is to add the column last. * `ALTER COLUMN' specifies a new default value for a column or removes the old default value. If the old default is removed and the column can be `NULL', the new default is `NULL'. If the column cannot be `NULL', *MySQL* assigns a default value. Default value assignment is described in *Note `CREATE TABLE': CREATE TABLE. * `DROP INDEX' removes an index. This is a *MySQL* extension to ANSI SQL92. * If columns are dropped from a table, the columns are also removed from any index of which they are a part. If all columns that make up an index are dropped, the index is dropped as well. * `DROP PRIMARY KEY' drops the primary index. If no such index exists, it drops the first `UNIQUE' index in the table. (*MySQL* marks the first `UNIQUE' key as the `PRIMARY KEY' if no `PRIMARY KEY' was specified explicitly.) * With the C API function `mysql_info()', you can find out how many records were copied, and (when `IGNORE' is used) how many records were deleted due to duplication of unique key values. * The `FOREIGN KEY', `CHECK' and `REFERENCES' clauses don't actually do anything. The syntax for them is provided only for compatibility, to make it easier to port code from other SQL servers and to run applications that create tables with references. *Note Missing functions::. Here is an example that shows some of the uses of `ALTER TABLE'. We begin with a table `t1' that is created as shown below: mysql> CREATE TABLE t1 (a INTEGER,b CHAR(10)); To rename the table from `t1' to `t2': mysql> ALTER TABLE t1 RENAME t2; To change column `a' from `INTEGER' to `TINYINT NOT NULL' (leaving the name the same), and to change column `b' from `CHAR(10)' to `CHAR(20)' as well as renaming it from `b' to `c': mysql> ALTER TABLE t2 MODIFY a TINYINT NOT NULL, CHANGE b c CHAR(20); To add a new `TIMESTAMP' column named `d': mysql> ALTER TABLE t2 ADD d TIMESTAMP; To add an index on column `d', and make column `a' the primary key: mysql> ALTER TABLE t2 ADD INDEX (d), ADD PRIMARY KEY (a); To remove column `c': mysql> ALTER TABLE t2 DROP COLUMN c; To add a new `AUTO_INCREMENT' integer column named `c': mysql> ALTER TABLE t2 ADD c INT UNSIGNED NOT NULL AUTO_INCREMENT, ADD INDEX (c); Note that we indexed `c', because `AUTO_INCREMENT' columns must be indexed, and also that we declare `c' as `NOT NULL', because indexed columns cannot be `NULL'. When you add an `AUTO_INCREMENT' column, column values are filled in with sequence numbers for you automatically. `OPTIMIZE TABLE' syntax ======================= OPTIMIZE TABLE tbl_name `OPTIMZE TABLE' should be used if you have deleted a large part of a table or if you have made many changes to a table with variable-length rows (tables that have `VARCHAR', `BLOB' or `TEXT' columns). Deleted records are maintained in a linked list and subsequent `INSERT' operations reuse old record positions. You can use `OPTIMIZE TABLE' to reclaim the unused space. `OPTIMIZE TABLE' works by making a temporary copy of the original table. The old table is copied to the new table (without the unused rows), then the original table is deleted and the new one is renamed. This is done in such a way that all updates are automatically redirected to the new table without any failed updates. While `OPTIMIZE TABLE' is executing, the original table is readable by other clients. Updates and writes to the table are stalled until the new table is ready. `DROP TABLE' syntax =================== DROP TABLE [IF EXISTS] tbl_name [, tbl_name,...] `DROP TABLE' removes one or more tables. All table data and the table definition are *removed*, so *be careful* with this command! In *MySQL* 3.22 or later, you can use the keywords `IF EXISTS' to prevent an error from occurring for tables that don't exist. `DELETE' syntax =============== DELETE [LOW_PRIORITY] FROM tbl_name [WHERE where_definition] [LIMIT rows] `DELETE' deletes rows from `tbl_name' that satisfy the condition given by `where_definition', and returns the number of records deleted. If you issue a `DELETE' with no `WHERE' clause, all rows are deleted. *MySQL* does this by recreating the table as an empty table, which is much faster than deleting each row. In this case, `DELETE' returns zero as the number of affected records. (*MySQL* can't return the number of rows that were actually deleted, since the recreate is done without opening the data files. As long as the table definition file `tbl_name.frm' is valid, the table can be recreated this way, even if the data or index files have become corrupted.). If you really want to know how many records are deleted when you are deleting all rows, and are willing to suffer a speed penalty, you can use a `DELETE' statement of this form: mysql> DELETE FROM tbl_name WHERE 1>0; Note that this is MUCH slower than `DELETE FROM tbl_name' with no `WHERE' clause, because it deletes rows one at a time. If you specify the keyword `LOW_PRIORITY', execution of the `DELETE' is delayed until no other clients are reading from the table. Deleted records are maintained in a linked list and subsequent `INSERT' operations reuse old record positions. To reclaim unused space and reduce file sizes, use the `OPTIMIZE TABLE' statement or the `isamchk' utility to reorganize tables. `OPTIMIZE TABLE' is easier, but `isamchk' is faster. *Note `OPTIMIZE TABLE': OPTIMIZE TABLE, and *Note Optimization::. The *MySQL*-specific `LIMIT rows' option to `DELETE' tells the server the maximum number of rows to be deleted before control is returned to the client. This can be used to ensure that a specific `DELETE' command doesn't take too much time. You can simply repeat the `DELETE' command until the number of affected rows is less than the `LIMIT' value. `SELECT' syntax =============== SELECT [STRAIGHT_JOIN] [SQL_SMALL_RESULT] [SQL_BIG_RESULT] [HIGH_PRIORITY] [DISTINCT | DISTINCTROW | ALL] select_expression,... [INTO OUTFILE 'file_name' export_options] [FROM table_references [WHERE where_definition] [GROUP BY col_name,...] [HAVING where_definition] [ORDER BY {unsigned_integer | col_name | formula} [ASC | DESC] ,...] [LIMIT [offset,] rows] [PROCEDURE procedure_name] ] `SELECT' is used to retrieve rows selected from one or more tables. `select_expression' indicates the columns you want to retrieve. `SELECT' may also be used to retrieve rows computed without reference to any table. For example: mysql> SELECT 1 + 1; -> 2 All keywords used must be given in exactly the order shown above. For example, a `HAVING' clause must come after any `GROUP BY' clause and before any `ORDER BY' clause. * A `SELECT' expression may be given an alias using `AS'. The alias is used as the expression's column name and can be used with `ORDER BY' or `HAVING' clauses. For example: mysql> select concat(last_name,', ',first_name) AS full_name from mytable ORDER BY full_name; * The `FROM table_references' clause indicates the tables from which to retrieve rows. If you name more than one table, you are performing a join. For information on join syntax, see *Note `JOIN': JOIN. * You can refer to a column as `col_name', `tbl_name.col_name' or `db_name.tbl_name.col_name'. You need not specify a `tbl_name' or `db_name.tbl_name' prefix for a column reference in a `SELECT' statement unless the reference would be ambiguous. See *Note Legal names::, for examples of ambiguity that require the more explicit column reference forms. * A table reference may be aliased using `tbl_name [AS] alias_name'. mysql> select t1.name, t2.salary from employee AS t1, info AS t2 where t1.name = t2.name; mysql> select t1.name, t2.salary from employee t1, info t2 where t1.name = t2.name; * Columns selected for output may be referred to in `ORDER BY' and `GROUP BY' clauses using column names, column aliases or column positions. Column positions begin with 1. mysql> select college, region, seed from tournament ORDER BY region, seed; mysql> select college, region AS r, seed AS s from tournament ORDER BY r, s; mysql> select college, region, seed from tournament ORDER BY 2, 3; To sort in reverse order, add the `DESC' (descending) keyword to the name of the column in the `ORDER BY' clause that you are sorting by. The default is ascending order; this may be specified explicitly using the `ASC' keyword. * The `HAVING' clause can refer to any column or alias named in the `select_expression'. It is applied last, just before items are sent to the client, with no optimization. Don't use `HAVING' for items that should be in the `WHERE' clause. For example, do not write this: mysql> select col_name from tbl_name HAVING col_name > 0; Write this instead: mysql> select col_name from tbl_name WHERE col_name > 0; In *MySQL* 3.22.5 or later, you can also write queries like this: mysql> select user,max(salary) from users group by user HAVING max(salary)>10; In older *MySQL* versions, you can write this instead: mysql> select user,max(salary) AS sum from users group by user HAVING sum>10; * `SQL_SMALL_RESULT', `SQL_BIG_RESULT', `STRAIGHT_JOIN' and `HIGH_PRIORITY' are *MySQL* extensions to ANSI SQL92. * `STRAIGHT_JOIN' forces the optimizer to join the tables in the order in which they are listed in the `FROM' clause. You can use this to speed up a query if the optimizer joins the tables in non-optimal order. *Note `EXPLAIN': EXPLAIN. * `SQL_SMALL_RESULT' can be used with `GROUP BY' or `DISTINCT' to tell the optimizer that the result set will be small. In this case, *MySQL* will use fast temporary tables to store the resulting table instead of using sorting. `SQL_SMALL_RESULT' is a *MySQL* * `SQL_BIG_RESULT' can be used with `GROUP BY' or `DISTINCT' to tell the optimizer that the result set will have many rows. In this case, *MySQL* will directly use disk based temporary tables if needed. `MySQL' in this case will prefer to do a sort instead doing a temporary table with a key on the `GROUP BY' elements. * `HIGH_PRIORITY' will give the `SELECT' higher priority than a statement that updates a table. You should only use this for queries that are very fast and must be done at once. A `SELECT HIGH_PRIORITY' query will run if the table is locked for read even if there is an update statement that is waiting for the table to be free. * The `LIMIT' clause can be used to constrain the number of rows returned by the `SELECT' statement. `LIMIT' takes one or two numeric arguments. If two arguments are given, the first specifies the offset of the first row to return, the second specifies the maximum number of rows to return. The offset of the initial row is 0 (not 1). mysql> select * from table LIMIT 5,10; # Retrieve rows 6-15 If one argument is given, it indicates the maximum number of rows to return. mysql> select * from table LIMIT 5; # Retrieve first 5 rows In other words, `LIMIT n' is equivalent to `LIMIT 0,n'. * The `SELECT ... INTO OUTFILE 'file_name'' form of `SELECT' writes the selected rows to a file. The file is created on the server host, and cannot already exist (among other things, this prevents database tables and files such as `/etc/passwd' from being destroyed). You must have the *file* privilege on the server host to use this form of `SELECT'. `SELECT ... INTO OUTFILE' is the complement of `LOAD DATA INFILE'; the syntax for the `export_options' part of the statement consists of the same `FIELDS' and `LINES' clauses that are used with the `LOAD DATA INFILE' statement. *Note `LOAD DATA': LOAD DATA. In the resulting text file, only the following characters are escaped by the `ESCAPED BY' character: * The `ESCAPED BY' character * The first character in `FIELDS TERMINATED BY' * The first character in `LINES TERMINATED BY' Additionally, `ASCII 0' is converted to `ESCAPED BY' followed by 0 (`ASCII 48'). The reason for the above is that you MUST escape any `FIELDS TERMINATED BY', `ESCAPED BY' or `LINES TERMINATED BY' characters to reliably be able to read the file back. `ASCII 0' is escaped to make it easier to view with some pagers. As the resulting file doesn't have to conform to the SQL syntax, nothing else need be escaped. `JOIN' syntax ============= *MySQL* supports the following `JOIN' syntaxes for use in `SELECT' statements: table_reference, table_reference table_reference [CROSS] JOIN table_reference table_reference INNER JOIN table_reference table_reference STRAIGHT_JOIN table_reference table_reference LEFT [OUTER] JOIN table_reference ON conditional_expr table_reference LEFT [OUTER] JOIN table_reference USING (column_list) table_reference NATURAL LEFT [OUTER] JOIN table_reference { oj table_reference LEFT OUTER JOIN table_reference ON conditional_expr } The last `LEFT OUTER JOIN' syntax shown above exists only for compatibility with ODBC. * A table reference may be aliased using `tbl_name AS alias_name' or `tbl_name alias_name'. mysql> select t1.name, t2.salary from employee AS t1, info AS t2 where t1.name = t2.name; * `INNER JOIN' and `,' (comma) are semantically equivalent. Both do a full join between the tables used. Normally, you specify how the tables should be linked in the `WHERE' condition. * The `ON' conditional is any conditional of the form that may be used in a `WHERE' clause. * If there is no matching record for the right table in a `LEFT JOIN', a row with all columns set to `NULL' is used for the right table. You can use this fact to find records in a table that have no counterpart in another table: mysql> select table1.* from table1 LEFT JOIN table2 ON table1.id=table2.id where table2.id is NULL; This example finds all rows in `table1' with an `id' value that is not present in `table2' (i.e., all rows in `table1' with no corresponding row in `table2'). This assumes that `table2.id' is declared `NOT NULL', of course. * The `USING' `(column_list)' clause names a list of columns that must exist in both tables. A `USING' clause such as: A LEFT JOIN B USING (C1,C2,C3,...) is defined to be semantically identical to an `ON' expression like this: A.C1=B.C1 AND A.C2=B.C2 AND A.C3=B.C3,... * The `NATURAL LEFT JOIN' of two tables is defined to be semantically equivalent to a `LEFT JOIN' with a `USING' clause that names all columns that exist in both tables. * `STRAIGHT_JOIN' is identical to `JOIN', except that the left table is always read before the right table. This can be used for those (few) cases where the join optimizer puts the tables in the wrong order. Some examples: mysql> select * from table1,table2 where table1.id=table2.id; mysql> select * from table1 LEFT JOIN table2 ON table1.id=table2.id; mysql> select * from table1 LEFT JOIN table2 USING (id); mysql> select * from table1 LEFT JOIN table2 ON table1.id=table2.id LEFT JOIN table3 ON table2.id=table3.id; *Note `LEFT JOIN' optimization: LEFT JOIN optimization. `INSERT' syntax =============== INSERT [LOW_PRIORITY | DELAYED] [IGNORE] [INTO] tbl_name [(col_name,...)] VALUES (expression,...),(...),... or INSERT [LOW_PRIORITY | DELAYED] [IGNORE] [INTO] tbl_name [(col_name,...)] SELECT ... or INSERT [LOW_PRIORITY | DELAYED] [IGNORE] [INTO] tbl_name SET col_name=expression, col_name=expression, ... `INSERT' inserts new rows into an existing table. The `INSERT ... VALUES' form of the statement inserts rows based on explicitly-specified values. The `INSERT ... SELECT' form inserts rows selected from another table or tables. The `INSERT ... VALUES' form with multiple value lists is supported in *MySQL* 3.22.5 or later. The `col_name=expression' syntax is supported in *MySQL* 3.22.10 or later. `tbl_name' is the table into which rows should be inserted. The column name list or the `SET' clause indicates which columns the statement specifies values for. * If you specify no column list for `INSERT ... VALUES' or `INSERT ... SELECT', values for all columns must be provided in the `VALUES()' list or by the `SELECT'. If you don't know the order of the columns in the table, use `DESCRIBE tbl_name' to find out. * Any column not explicitly given a value is set to its default value. For example, if you specify a column list that doesn't name all the columns in the table, unnamed columns are set to their default values. Default value assignment is described in *Note `CREATE TABLE': CREATE TABLE. * An `expression' may refer to any column that was set earlier in a value list. For example, you can say this: mysql> INSERT INTO tbl_name (col1,col2) VALUES(15,col1*2); But not this: mysql> INSERT INTO tbl_name (col1,col2) VALUES(col2*2,15); * If you specify the keyword `LOW_PRIORITY', execution of the `INSERT' is delayed until no other clients are reading from the table. * If you specify the keyword `IGNORE' in an `INSERT' with many value rows, any rows which duplicate an existing `PRIMARY' or `UNIQUE' key in the table are ignored and are not inserted. If you do not specify `IGNORE', the insert is aborted if there is any row that duplicates an existing key value. You can check with the C API function `mysql_info()' how many rows were inserted into the table. * If *MySQL* was configured using the `DONT_USE_DEFAULT_FIELDS' option, `INSERT' statements generate an error unless you explicitly specify values for all columns that require a non-`NULL' value. *Note `configure' options: configure options. * The following conditions hold for a `INSERT INTO ... SELECT' statement: - The query cannot contain an `ORDER BY' clause. - The target table of the `INSERT' statement cannot appear in the `FROM' clause of the `SELECT' part of the query, because it's forbidden in ANSI SQL to `SELECT' from the same table into which you are `INSERT'ing. (The problem is that the `SELECT' possibly would find records that were inserted earlier during the same run. When using sub-select clauses, the situation could easily be very confusing!) - `AUTO_INCREMENT' columns work as usual. If you use `INSERT ... SELECT' or a `INSERT ... VALUES' statement with multiple value lists, you can use the C API function `mysql_info()' to get information about the query. The format of the information string is shown below: Records: 100 Duplicates: 0 Warnings: 0 `Duplicates' indicates the number of rows that couldn't be inserted because they would duplicate some existing unique index value. `Warnings' indicates the number of attempts to insert column values that were problematic in some way. Warnings can occur under any of the following conditions: * Inserting `NULL' into a column that has been declared `NOT NULL'. The column is set to its default value. * Setting a numeric column to a value that lies outside the column's range. The value is clipped to the appropriate endpoint of the range. * Setting a numeric column to a value such as `'10.34 a''. The trailing garbage is stripped and the remaining numeric part is inserted. If the value doesn't make sense as a number at all, the column is set to `0'. * Inserting a string into a `CHAR', `VARCHAR', `TEXT' or `BLOB' column that exceeds the column's maximum length. The value is truncated to the column's maximum length. * Inserting a value into a date or time column that is illegal for the column type. The column is set to the appropriate "zero" value for the type. The `DELAYED' option for the `INSERT' statement is a *MySQL*-specific option that is very useful if you have clients that can't wait for the `INSERT' to complete. This is common when you use *MySQL* for logging and you also periodically run `SELECT' statements that take a long time to complete. `DELAYED' was introduced in *MySQL* 3.22.15. It is a *MySQL* extension to ANSI SQL92. Another major benefit of using `INSERT DELAYED' is that inserts from many clients are bundled together and written in one block. This is much faster than doing many separate inserts. Note that currently the queued rows are only stored in memory until they are inserted into the table. This means that if you kill `mysqld' the hard way (`kill -9') or if `mysqld' dies unexpectedly, any queued rows that weren't written to disk are lost! The following happens when you use the `DELAYED' option to `INSERT' or `REPLACE'. In this description, the "thread" is the thread that received an `INSERT DELAYED' command and "handler" is the thread that handles all `INSERT DELAYED' statements for a particular table. * When a thread executes a `DELAYED' statement for a table, a handler thread is created to process all `DELAYED' statements for the table, if no such handler already exists. * The thread checks whether or not the handler has acquired a `DELAYED' lock already; if not, it tells the handler thread to do so. The `DELAYED' lock can be obtained even if other threads have a `READ' or `WRITE' lock on the table. However, the handler will wait for all `ALTER TABLE' locks or `FLUSH TABLES' to ensure that the table structure is up to date. * The thread executes the `INSERT' statement but instead of writing the row to the table it puts a copy of the final row into a queue that is managed by the handler thread. Any syntax errors are noticed by the thread and reported to the client program. * The client can't report the number of duplicates or the `AUTO_INCREMENT' value for the resulting row; it can't obtain them from the server, because the `INSERT' returns before the insert operation has been completed. If you use the C API, the `mysql_info()' function doesn't return anything meaningful, for the same reason. * The update log is updated by the handler thread when the row is inserted into the table. In case of multiple-row inserts, the update log is updated when the first row is inserted. * After every `delayed_insert_limit' rows are written, the handler checks whether or not any `SELECT' statements are still pending. If so, it allows these to execute before continuing. * When the handler has no more rows in its queue, the table is unlocked. If no new `INSERT DELAYED' commands are received within `delayed_insert_timeout' seconds, the handler terminates. * If more than `delayed_queue_size' rows are pending already in a specific handler queue, the thread waits until there is room in the queue. This is useful to ensure that the `mysqld' server doesn't use all memory for the delayed memory queue. * The handler thread will show up in the *MySQL* process list with `delayed_insert' in the `Command' column. It will be killed if you execute a `FLUSH TABLES' command or kill it with `KILL thread_id'. However, it will first store all queued rows into the table before exiting. During this time it will not accept any new `INSERT' commands from another thread. If you execute an `INSERT DELAYED' command after this, a new handler thread will be created. * Note that the above means that `INSERT DELAYED' commands have higher priority than normal `INSERT' commands if there is an `INSERT DELAYED' handler already running! Other update commands will have to wait until the `INSERT DELAY' queue is empty, someone kills the handler thread (with `KILL thread_id') or someone executes `FLUSH TABLES'. * The following status variables provide information about `INSERT DELAYED' commands: `Delayed_insert_threads'Number of handler threads `Delayed_writes' Number of rows written with `INSERT DELAYED' `Not_flushed_delayed_rows'Number of rows waiting to be written You can view these variables by issuing a `SHOW STATUS' statement or by executing a `mysqladmin extended-status' command. `REPLACE' syntax ================ REPLACE [LOW_PRIORITY | DELAYED] [INTO] tbl_name [(col_name,...)] VALUES (expression,...) or REPLACE [LOW_PRIORITY | DELAYED] [INTO] tbl_name [(col_name,...)] SELECT ... or REPLACE [LOW_PRIORITY | DELAYED] [INTO] tbl_name SET col_name=expression, col_name=expression,... `REPLACE' works exactly like `INSERT', except that if an old record in the table has the same value as a new record on a unique index, the old record is deleted before the new record is inserted. *Note `INSERT': INSERT. `LOAD DATA INFILE' syntax ========================= LOAD DATA [LOW_PRIORITY] [LOCAL] INFILE 'file_name.txt' [REPLACE | IGNORE] INTO TABLE tbl_name [FIELDS [TERMINATED BY '\t'] [OPTIONALLY] ENCLOSED BY ''] [ESCAPED BY '\\' ]] [LINES TERMINATED BY '\n'] [IGNORE number LINES] [(col_name,...)] The `LOAD DATA INFILE' statement reads rows from a text file into a table at a very high speed. If the `LOCAL' keyword is specified, the file is read from the client host. If `LOCAL' is not specified, the file must be located on the server. (`LOCAL' is available in *MySQL* 3.22.6 or later.) For security reasons, when reading text files located on the server, the files must either reside in the database directory or be readable by all. Also, to use `LOAD DATA INFILE' on server files, you must have the *file* privilege on the server host. *Note Privileges provided::. If you specify the keyword `LOW_PRIORITY', execution of the `LOAD DATA' statement is delayed until no other clients are reading from the table. Using `LOCAL' will be a bit slower than letting the server access the files directly, since the contents of the file must travel from the client host to the server host. On the other hand, you do not need the *file* privilege to load local files. You can also load data files by using the `mysqlimport' utility; it operates by sending a `LOAD DATA INFILE' command to the server. The `--local' option causes `mysqlimport' to read data files from the client host. You can specify the `--compress' option to get better performance over slow networks if the client and server support the compressed protocol. When locating files on the server host, the server uses the following rules: * If an absolute pathname is given, the server uses the pathname as is. * If a relative pathname with one or more leading components is given, the server searches for the file relative to the server's data directory. * If a filename with no leading components is given, the server looks for the file in the database directory of the current database. Note that these rules mean a file given as `./myfile.txt' is read from the server's data directory, whereas a file given as `myfile.txt' is read from the database directory of the current database. Note also that for statements such as those below, the file is read from the database directory for `db1', not `db2': mysql> USE db1; mysql> LOAD DATA INFILE "./data.txt" INTO TABLE db2.my_table; The `REPLACE' and `IGNORE' keywords control handling of input records that duplicate existing records on unique key values. If you specify `REPLACE', new rows replace existing rows that have the same unique key value. If you specify `IGNORE', input rows that duplicate an existing row on a unique key value are skipped. If you don't specify either option, an error occurs when a duplicate key value is found, and the rest of the text file is ignored. If you load data from a local file using the `LOCAL' keyword, the server has no way to stop transmission of the file in the middle of the operation, so the default bahavior is the same as if `IGNORE' is specified. `LOAD DATA INFILE' is the complement of `SELECT ... INTO OUTFILE'. *Note `SELECT': SELECT. To write data from a database to a file, use `SELECT ... INTO OUTFILE'. To read the file back into the database, use `LOAD DATA INFILE'. The syntax of the `FIELDS' and `LINES' clauses is the same for both commands. Both clauses are optional, but `FIELDS' must precede `LINES' if both are specified. If you specify a `FIELDS' clause, each of its subclauses (`TERMINATED BY', `[OPTIONALLY] ENCLOSED BY' and `ESCAPED BY') is also optional, except that you must specify at least one of them. If you don't specify a `FIELDS' clause, the defaults are the same as if you had written this: FIELDS TERMINATED BY '\t' ENCLOSED BY '' ESCAPED BY '\\' If you don't specify a `LINES' clause, the default is the same as if you had written this: LINES TERMINATED BY '\n' In other words, the defaults cause `LOAD DATA INFILE' to act as follows when reading input: * Look for line boundaries at newlines * Break lines into fields at tabs * Do not expect fields to be enclosed within any quoting characters * Interpret occurrences of tab, newline or `\' preceded by `\' as literal characters that are part of field values Conversely, the defaults cause `SELECT ... INTO OUTFILE' to act as follows when writing output: * Write tabs between fields * Do not enclose fields within any quoting characters * Use `\' to escape instances of tab, newline or `\' that occur within field values * Write newlines at the ends of lines Note that to write `FIELDS ESCAPED BY '\\'', you must specify two backslashes for the value to be read as a single backslash. The `IGNORE number LINES' option can be used to ignore a header of column names at the start of the file: mysql> LOAD DATA INFILE "/tmp/file_name" into table test IGNORE 1 LINES; When you use `SELECT ... INTO OUTFILE' in tandem with `LOAD DATA INFILE' to write data from a database into a file and then read the file back into the database later, the field and line handling options for both commands must match. Otherwise, `LOAD DATA INFILE' will not interpret the contents of the file properly. Suppose you use `SELECT ... INTO OUTFILE' to write a file with fields delimited by commas: mysql> SELECT * FROM table1 INTO OUTFILE 'data.txt' FIELDS TERMINATED BY ',' FROM ... To read the comma-delimited file back in, the correct statement would be: mysql> LOAD DATA INFILE 'data.txt' INTO TABLE table2 FIELDS TERMINATED BY ','; If instead you tried to read in the file with the statement shown below, it wouldn't work because it instructs `LOAD DATA INFILE' to look for tabs between fields: mysql> LOAD DATA INFILE 'data.txt' INTO TABLE table2 FIELDS TERMINATED BY '\t'; The likely result is that each input line would be interpreted as a single field. `LOAD DATA INFILE' can be used to read files obtained from external sources, too. For example, a file in dBASE format will have fields separated by commas and enclosed in double quotes. If lines in the file are terminated by newlines, the command shown below illustrates the field and line handling options you would use to load the file: mysql> LOAD DATA INFILE 'data.txt' INTO TABLE tbl_name FIELDS TERMINATED BY ',' ENCLOSED BY '"' LINES TERMINATED BY '\n'; Any of the field or line handling options may specify an empty string (`'''). If not empty, the `FIELDS [OPTIONALLY] ENCLOSED BY' and `FIELDS ESCAPED BY' values must be a single character. The `FIELDS TERMINATED BY' and `LINES TERMINATED BY' values may be more than one character. For example, to write lines that are terminated by carriage return-linefeed pairs, or to read a file containing such lines, specify a `LINES TERMINATED BY '\r\n'' clause. `FIELDS [OPTIONALLY] ENCLOSED BY' controls quoting of fields. For output (`SELECT ... INTO OUTFILE'), if you omit the word `OPTIONALLY', all fields are enclosed by the `ENCLOSED BY' character. An example of such output (using a comma as the field delimiter) is shown below: "1","a string","100.20" "2","a string containing a , comma","102.20" "3","a string containing a \" quote","102.20" "4","a string containing a \", quote and comma","102.20" If you specify `OPTIONALLY', the `ENCLOSED BY' character is used only to enclose `CHAR' and `VARCHAR' fields: 1,"a string",100.20 2,"a string containing a , comma",102.20 3,"a string containing a \" quote",102.20 4,"a string containing a \", quote and comma",102.20 Note that occurrences of the `ENCLOSED BY' character within a field value are escaped by prefixing them with the `ESCAPED BY' character. Also note that if you specify an empty `ESCAPED BY' value, it is possible to generate output that cannot be read properly by `LOAD DATA INFILE'. For example, the output just shown above would appear as shown below if the escape character is empty. Observe that the second field in the fourth line contains a comma following the quote, which (erroneously) appears to terminate the field: 1,"a string",100.20 2,"a string containing a , comma",102.20 3,"a string containing a " quote",102.20 4,"a string containing a ", quote and comma",102.20 For input, the `ENCLOSED BY' character, if present, is stripped from the ends of field values. (This is true whether or not `OPTIONALLY' is specified; `OPTIONALLY' has no effect on input interpretation.) Occurrences of the `ENCLOSED BY' character preceded by the `ESCAPED BY' character are interpreted as part of the current field value. In addition, duplicated `ENCLOSED BY' characters occurring within fields are interpreted as single `ENCLOSED BY' characters if the field itself starts with that character. For example, if `ENCLOSED BY '"'' is specified, quotes are handled as shown below: "The ""BIG"" boss" -> The "BIG" boss The "BIG" boss -> The "BIG" boss The ""BIG"" boss -> The ""BIG"" boss `FIELDS ESCAPED BY' controls how to write or read special characters. If the `FIELDS ESCAPED BY' character is not empty, it is used to prefix the following characters on output: * The `FIELDS ESCAPED BY' character * The `FIELDS [OPTIONALLY] ENCLOSED BY' character * The first character of the `FIELDS TERMINATED BY' and `LINES TERMINATED BY' values * ASCII `0' (what is actually written following the escape character is ASCII `'0'', not a zero-valued byte) If the `FIELDS ESCAPED BY' character is empty, no characters are escaped. It is probably not a good idea to specify an empty escape character, particularly if field values in your data contain any of the characters in the list just given. For input, if the `FIELDS ESCAPED BY' character is not empty, occurrences of that character are stripped and the following character is taken literally as part of a field value. The exceptions are an escaped `0' or `N' (e.g., `\0' or `\N' if the escape character is `\'). These sequences are interpreted as ASCII `0' (a zero-valued byte) and `NULL'. See below for the rules on `NULL' handling. For more information about `\'-escape syntax, see *Note Literals::. In certain cases, field and line handling options interact: * If `LINES TERMINATED BY' is an empty string and `FIELDS TERMINATED BY' is non-empty, lines are also terminated with `FIELDS TERMINATED BY'. * If the `FIELDS TERMINATED BY' and `FIELDS ENCLOSED BY' values are both empty (`'''), a fixed-row (non-delimited) format is used. With fixed-row format, no delimiters are used between fields. Instead, column values are written and read using the "display" widths of the columns. For example, if a column is declared as `INT(7)', values for the column are written using 7-character fields. On input, values for the column are obtained by reading 7 characters. Fixed-row format also affects handling of `NULL' values; see below. Handling of `NULL' values varies, depending on the `FIELDS' and `LINES' options you use: * For the default `FIELDS' and `LINES' values, `NULL' is written as `\N' for output and `\N' is read as `NULL' for input (assuming the `ESCAPED BY' character is `\'). * If `FIELDS ENCLOSED BY' is not empty, a field containing the literal word `NULL' as its value is read as a `NULL' value (this differs from the word `NULL' enclosed within `FIELDS ENCLOSED BY' characters, which is read as the string `'NULL''). * If `FIELDS ESCAPED BY' is empty, `NULL' is written as the word `NULL'. * With fixed-row format (which happens when `FIELDS TERMINATED BY' and `FIELDS ENCLOSED BY' are both empty), `NULL' is written as an empty string. Note that this causes both `NULL' values and empty strings in the table to be indistinguishable when written to the file since they are both written as empty strings. If you need to be able to tell the two apart when reading the file back in, you should not use fixed-row format. Some cases are not supported by `LOAD DATA INFILE': * Fixed-size rows (`FIELDS TERMINATED BY' and `FIELDS ENCLOSED BY' both empty) and `BLOB' or `TEXT' columns. * If you specify one separator that is the same as or a prefix of another, `LOAD DATA INFILE' won't be able to interpret the input properly. For example, the following `FIELDS' clause would cause problems: FIELDS TERMINATED BY '"' ENCLOSED BY '"' * If `FIELDS ESCAPED BY' is empty, a field value that contains an occurrence of `FIELDS ENCLOSED BY' or `LINES TERMINATED BY' followed by the `FIELDS TERMINATED BY' value will cause `LOAD DATA INFILE' to stop reading a field or line too early. This happens because `LOAD DATA INFILE' cannot properly determine where the field or line value ends. The following example loads all columns of the `persondata' table: mysql> LOAD DATA INFILE 'persondata.txt' INTO TABLE persondata; No field list is specified, so `LOAD DATA INFILE' expects input rows to contain a field for each table column. The default `FIELDS' and `LINES' values are used. If you wish to load only some of a table's columns, specify a field list: mysql> LOAD DATA INFILE 'persondata.txt' INTO TABLE persondata (col1,col2,...); You must also specify a field list if the order of the fields in the input file differs from the order of the columns in the table. Otherwise, *MySQL* cannot tell how to match up input fields with table columns. If a row has too few fields, the columns for which no input field is present are set to default values. Default value assignment is described in *Note `CREATE TABLE': CREATE TABLE. An empty field value is interpreted differently than if the field value is missing: * For string types, the column is set to the empty string. * For numeric types, the column is set to `0'. * For date and time types, the column is set to the appropriate "zero" value for the type. *Note Date and time types::. `TIMESTAMP' columns are only set to the current date and time if there is a `NULL' value for the column, or (for the first `TIMESTAMP' column only) if the `TIMESTAMP' column is left out from the field list when a field list is specified. If an input row has too many fields, the extra fields are ignored and the number of warnings is incremented. `LOAD DATA INFILE' regards all input as strings, so you can't use numeric values for `ENUM' or `SET' columns the way you can with `INSERT' statements. All `ENUM' and `SET' values must be specified as strings! If you are using the C API, you can get information about the query by calling the API function `mysql_info()' when the `LOAD DATA INFILE' query finishes. The format of the information string is shown below: Records: 1 Deleted: 0 Skipped: 0 Warnings: 0 Warnings occur under the same circumstances as when values are inserted via the `INSERT' statement (*note `INSERT': INSERT.), except that `LOAD DATA INFILE' also generates warnings when there are too few or too many fields in the input row. The warnings are not stored anywhere; the number of warnings can only be used as an indication if everything went well. If you get warnings and want to know exactly why you got them, one way to do this is to use `SELECT ... INTO OUTFILE' into another file and compare this to your original input file. For more information about the efficiency of `INSERT' versus `LOAD DATA INFILE' and speeding up `LOAD DATA INFILE', see *Note Table efficiency::. `UPDATE' syntax =============== UPDATE [LOW_PRIORITY] tbl_name SET col_name1=expr1,col_name2=expr2,... [WHERE where_definition] [LIMIT #] `UPDATE' updates columns in existing table rows with new values. The `SET' clause indicates which columns to modify and the values they should be given. The `WHERE' clause, if given, specifies which rows should be updated. Otherwise all rows are updated. If you specify the keyword `LOW_PRIORITY', execution of the `UPDATE' is delayed until no other clients are reading from the table. If you access a column from `tbl_name' in an expression, `UPDATE' uses the current value of the column. For example, the following statement sets the `age' column to one more than its current value: mysql> UPDATE persondata SET age=age+1; `UPDATE' assignments are evaluated from left to right. For example, the following statement doubles the `age' column, then increments it: mysql> UPDATE persondata SET age=age*2, age=age+1; If you set a column to the value it currently has, *MySQL* notices this and doesn't update it. `UPDATE' returns the number of rows that were actually changed. In *MySQL* 3.22 or later, the C API function `mysql_info()' returns the number of rows that were matched and updated and the number of warnings that occurred during the `UPDATE'. In *MySQL* 3.23 you can use `LIMIT #' to ensure that only a given number of rows are changed. `USE' syntax ============ USE db_name The `USE db_name' statement tells *MySQL* to use the `db_name' database as the default database for subsequent queries. The database remains current until the end of the session, or until another `USE' statement is issued: mysql> USE db1; mysql> SELECT count(*) FROM mytable; # selects from db1.mytable mysql> USE db2; mysql> SELECT count(*) FROM mytable; # selects from db2.mytable Making a particular database current by means of the `USE' statement does not preclude you from accessing tables in other databases. The example below accesses the `author' table from the `db1' database and the `editor' table from the `db2' database: mysql> USE db1; mysql> SELECT author_name,editor_name FROM author,db2.editor WHERE author.editor_id = db2.editor.editor_id; The `USE' statement is provided for Sybase compatibility. `FLUSH' syntax (clearing caches) ================================ FLUSH flush_option [,flush_option] You should use the `FLUSH' command if you want to clear some of the internal caches *MySQL* uses. To execute `FLUSH', you must have the *reload* privilege. `flush_option' can be any of the following: `HOSTS' Empties the host cache tables. You should flush the host tables if some of your hosts change IP number or if you get the error message `Host ... is blocked'. When more than `max_connect_errors' errors occur in a row for a given host while connection to the *MySQL* server, *MySQL* assumes something is wrong and blocks the host from further connection requests. Flushing the host tables allows the host to attempt to connect again. *Note Blocked host::.) You can start `mysqld' with `-O max_connection_errors=999999999' to avoid this error message. `LOGS' Closes and reopens the standard and update log files. If you have specified the update log file without an extension, the extension number of the new update log file will be incremented by one relative to the previous file. `PRIVILEGES'Reloads the privileges from the grant tables in the `mysql' database. `TABLES' Closes all open tables. `STATUS' Resets most status variables to zero. You can also access each of the commands shown above with the `mysqladmin' utility, using the `flush-hosts', `flush-logs', `reload' or `flush-tables' commands. `KILL' syntax ============= KILL thread_id Each connection to `mysqld' runs in a separate thread. You can see which threads are running with the `SHOW PROCESSLIST' command, and kill a thread with the `KILL thread_id' command. If you have the *process* privilege, you can see and kill all threads. Otherwise, you can see and kill only your own threads. You can also use the `mysqladmin processlist' and `mysqladmin kill' commands to examine and kill threads. `SHOW' syntax (Get information about tables, columns,...) ========================================================= SHOW DATABASES [LIKE wild] or SHOW TABLES [FROM db_name] [LIKE wild] or SHOW COLUMNS FROM tbl_name [FROM db_name] [LIKE wild] or SHOW INDEX FROM tbl_name [FROM db_name] or SHOW STATUS or SHOW VARIABLES [LIKE wild] or SHOW PROCESSLIST or SHOW TABLE STATUS [FROM db_name] [LIKE wild] or SHOW GRANTS FOR user `SHOW' provides information about databases, tables, columns or the server. If the `LIKE wild' part is used, the `wild' string can be a string that uses the SQL `%' and `_' wildcard characters. You can use `db_name.tbl_name' as an alternative to the `tbl_name FROM db_name' syntax. These two statements are equivalent: mysql> SHOW INDEX FROM mytable FROM mydb; mysql> SHOW INDEX FROM mydb.mytable; `SHOW DATABASES' lists the databases on the *MySQL* server host. You can also get this list using the `mysqlshow' command. `SHOW TABLES' lists the tables in a given database. You can also get this list using the `mysqlshow db_name' command. *Note:* If a user doesn't have any privileges for a table, the table will not show up in the output from `SHOW TABLES' or `mysqlshow db_name'. `SHOW COLUMNS' lists the columns in a given table. If the column types are different than you expect them to be based on a `CREATE TABLE' statement, note that MySQL sometimes changes column types. *Note Silent column changes::. The `DESCRIBE' statement provides information similar to `SHOW COLUMNS'. *Note `DESCRIBE': DESCRIBE. `SHOW TABLE STATUS' (new in version 3.23) works likes `SHOW STATUS', but provides a lot of information about each table. You can also get this list using the `mysqlshow --status db_name' command. The following columns are returned: *Column* *Meaning* `Name' Name of the table `Type' Type of table (NISAM, MyISAM or HEAP) `Row_format' The row storage format (Fixed, Dynamic, or Compressed) `Rows' Number of rows `Avg_row_length' Average row length `Data_length' Length of the data file `Max_data_length' Max length of the data file `Index_length' Length of the index file `Data_free' Number of allocated but not used bytes `Auto_increment' Next autoincrement value `Create_time' When the table was created `Update_time' When the data file was last updated `Check_time' When one last run a check on the table `Create_options' Extra options used with `CREATE TABLE' `Comment' The comment used when creating the table (or some information why MySQL couldn't access the table information). `SHOW FIELDS' is a synonym for `SHOW COLUMNS' and `SHOW KEYS' is a synonym for `SHOW INDEX'. You can also list a table's columns or indexes with `mysqlshow db_name tbl_name' or `mysqlshow -k db_name tbl_name'. `SHOW INDEX' returns the index information in a format that closely resembles the `SQLStatistics' call in ODBC. The following columns are returned: *Column* *Meaning* `Table' Name of the table `Non_unique' 0 if the index can't contain duplicates. `Key_name' Name of the index `Seq_in_index' Column sequence number in index, starting with 1. `Column_name' Column name. `Collation' How the column is sorted in the index. In *MySQL*, this can have values `A' (Ascending) or `NULL' (Not sorted). `Cardinality' Number of unique values in the index. This is updated by running `isamchk -a'. `Sub_part' Number of indexed characters if the column is only partly indexed. `NULL' if the entire key is indexed. `SHOW STATUS' provides server status information (like `mysqladmin extended-status'). The output resembles that shown below, though the format and numbers may differ somewhat: +--------------------------+--------+ | Variable_name | Value | +--------------------------+--------+ | Aborted_clients | 0 | | Aborted_connects | 0 | | Connections | 17 | | Created_tmp_tables | 0 | | Delayed_insert_threads | 0 | | Delayed_writes | 0 | | Delayed_errors | 0 | | Flush_commands | 2 | | Handler_delete | 2 | | Handler_read_first | 0 | | Handler_read_key | 1 | | Handler_read_next | 0 | | Handler_read_rnd | 35 | | Handler_update | 0 | | Handler_write | 2 | | Key_blocks_used | 0 | | Key_read_requests | 0 | | Key_reads | 0 | | Key_write_requests | 0 | | Key_writes | 0 | | Max_used_connections | 1 | | Not_flushed_key_blocks | 0 | | Not_flushed_delayed_rows | 0 | | Open_tables | 1 | | Open_files | 2 | | Open_streams | 0 | | Opened_tables | 11 | | Questions | 14 | | Slow_queries | 0 | | Threads_connected | 1 | | Threads_running | 1 | | Uptime | 149111 | +--------------------------+--------+ The status variables listed above have the following meaning: `Aborted_clients' Number of connections that has been aborted because the client has died without closing the connection properly. `Aborted_connects' Number of tries to connect to the MySQL server that has failed. `Connections' Number of connection attempts to the MySQL server. `Created_tmp_tables' Number of implicit temporary tables that has been created while executing statements. `Delayed_insert_threads' Number of delayed insert handler threads in use. `Delayed_writes' Number of rows written with `INSERT DELAYED'. `Delayed_errors' Number of rows written with `INSERT DELAYED' for which some error occurred (probably `duplicate key'). `Flush_commands' Number of executed `FLUSH' commands. `Handler_delete' Number of requests to delete a row from a table. `Handler_read_first' Number of requests to read the first row in a table. `Handler_read_key' Number of requests to read a row based on a key. `Handler_read_next' Number of requests to read next row in key order. `Handler_read_rnd' Number of requests to read a row based on a fixed position. `Handler_update' Number of requests to update a row in a table. `Handler_write' Number of requests to insert a row in a table. `Key_blocks_used' The number of used blocks in the key cache. `Key_read_requests' The number of requests to read a key block from the cache. `Key_reads' The number of physical reads of a key block from disk. `Key_write_requests' The number of requests to write a key block to the cache. `Key_writes' The number of physical writes of a key block to disk. `Max_used_connections' The maximum number of connections that has been in use simultaneously. `Not_flushed_key_blocks' Keys blocks in the key cache that has changed but hasn't yet been flushed to disk. `Not_flushed_delayed_rows'Number of rows waiting to be written in `INSERT DELAY' queues. `Open_tables' Number of tables that are open. `Open_files' Number of files that are open. `Open_streams' Number of streams that are open (used mainly for logging) `Opened_tables' Number of tables that has been opened. `Questions' Number of queries sent to the server. `Slow_queries' Number of queries that has taken more than `long_query_time' `Threads_connected' Number of currently open connections. `Threads_running' Number of threads that are not sleeping. `Uptime' How many seconds the server has been up. Some comments about the above: * If `Opened_tables' is big, then your `table_cache' variable is probably too small. * If `key_reads' is big, then your `key_cache' is probably too small. The cache hit rate can be calculated with `key_reads'/`key_read_requests'. * If `Handler_read_rnd' is big, then you have a probably a lot of queries that requires MySQL to scan whole tables or you have joins that doesn't use keys properly. `SHOW VARIABLES' shows the values of the some of *MySQL* system variables. You can also get this information using the `mysqladmin variables' command. If the default values are unsuitable, you can set most of these variables using command-line options when `mysqld' starts up. The output resembles that shown below, though the format and numbers may differ somewhat: +------------------------+--------------------------+ | Variable_name | Value | +------------------------+--------------------------+ | back_log | 5 | | connect_timeout | 5 | | basedir | /my/monty/ | | datadir | /my/monty/data/ | | delayed_insert_limit | 100 | | delayed_insert_timeout | 300 | | delayed_queue_size | 1000 | | join_buffer_size | 131072 | | flush_time | 0 | | key_buffer_size | 1048540 | | language | /my/monty/share/english/ | | log | OFF | | log_update | OFF | | long_query_time | 10 | | low_priority_updates | OFF | | max_allowed_packet | 1048576 | | max_connections | 100 | | max_connect_errors | 10 | | max_delayed_threads | 20 | | max_heap_table_size | 16777216 | | max_join_size | 4294967295 | | max_sort_length | 1024 | | max_tmp_tables | 32 | | net_buffer_length | 16384 | | port | 3306 | | protocol-version | 10 | | record_buffer | 131072 | | skip_locking | ON | | socket | /tmp/mysql.sock | | sort_buffer | 2097116 | | table_cache | 64 | | thread_stack | 131072 | | tmp_table_size | 1048576 | | tmpdir | /machine/tmp/ | | version | 3.23.0-alpha-debug | | wait_timeout | 28800 | +------------------------+--------------------------+ *Note Server parameters: Server parameters. `SHOW PROCESSLIST' shows you which threads are running. You can also get this information using the `mysqladmin processlist' command. If you have the *process* privilege, you can see all threads. Otherwise, you can see only your own threads. *Note `KILL': KILL. `SHOW GRANTS FOR user' lists the grant commands that must be issued to duplicate the grants for a user. mysql> SHOW GRANTS FOR root@localhost; +---------------------------------------------------------------------+ | Grants for root@localhost | +---------------------------------------------------------------------+ | GRANT ALL PRIVILEGES ON *.* TO 'root''localhost' WITH GRANT OPTION | +---------------------------------------------------------------------+ `EXPLAIN' syntax (Get information about a `SELECT') =================================================== EXPLAIN tbl_name or EXPLAIN SELECT select_options `EXPLAIN tbl_name' is a synonym for `DESCRIBE tbl_name' or `SHOW COLUMNS FROM tbl_name'. When you precede a `SELECT' statement with the keyword `EXPLAIN', *MySQL* explains how it would process the `SELECT', providing information about how tables are joined and in which order. With the help of `EXPLAIN', you can see when you must add indexes to tables to get a faster `SELECT' that uses indexes to find the records. You can also see if the optimizer joins the tables in an optimal order. To force the optimizer to use a specific join order for a `SELECT' statement, add a `STRAIGHT_JOIN' clause. For non-simple joins, `EXPLAIN' returns a row of information for each table used in the `SELECT' statement. The tables are listed in the order they would be read. *MySQL* resolves all joins using a single-sweep multi-join method. This means that *MySQL* reads a row from the first table, then finds a matching row in the second table, then in the third table and so on. When all tables are processed, it outputs the selected columns and backtracks through the table list until a table is found for which there are more matching rows. The next row is read from this table and the process continues with the next table. Output from `EXPLAIN' includes the following columns: `table' The table to which the row of output refers. `type' The join type. Information about the various types is given below. `possible_keys' The `possible_keys' column indicates which indexes *MySQL* could use to find the rows in the table. If this column is empty, there are no relevant indexes. In this case, you may be able to improve the performance of your query by examining the `WHERE' clause to see if it refers to some column or columns that would be suitable for indexing. If so, create an appropriate index and check the query with `EXPLAIN' again. To see what indexes a table has, use `SHOW INDEX FROM tbl_name'. `key' The `key' column indicates the key that *MySQL* actually decided to use. The key is `NULL' if no index was chosen. `key_len' The `key_len' column indicates the length of the key that *MySQL* decided to use. The length is `NULL' if the `key' is `NULL'. `ref' The `ref' column shows which columns or constants are used with the `key' to select rows from the table. `rows' The `rows' column indicates the number of rows *MySQL* must examine to execute the query. `Extra' If the `Extra' column includes the text `Only index', this means that information is retrieved from the table using only information in the index tree. Normally, this is much