MySQL is a relational database management system (RDBMS)[1] which has more than 11 million installations.[2] The program runs as a server providing multi-user access to a number of databases. MySQL is owned and sponsored by a single for-profit firm, the Swedish company MySQL AB, now a subsidiary of Sun Microsystems,[3] which holds the copyright to most of the codebase. The project's source code is available under terms of the GNU General Public License, as well as under a variety of proprietary agreements. "MySQL" is officially pronounced /maɪˌɛskjuːˈɛl/[4] (My S Q L), not "My sequel" /maɪˈsiːkwəl/. This adheres to the official ANSI pronunciation; SEQUEL was an earlier IBM database language, a predecessor to the SQL language.[5] The company does not take issue with the pronunciation "My sequel" or other local variations.[4] Uses MySQL is popular for web applications and acts as the database component of the LAMP, BAMP, MAMP, and WAMP platforms (Linux/BSD/Mac/Windows-Apache-MySQL-PHP/Perl/Python), and for open-source bug tracking tools like Bugzilla. Its popularity for use with web applications is closely tied to the popularity of PHP and Ruby on Rails, which are often combined with MySQL. Wikipedia runs on MediaWiki software, which is written in PHP and uses a MySQL database. Several high-traffic web sites use MySQL for its data storage and logging of user data, including Flickr, Facebook,[6][7] Wikipedia, Google,[8] Nokia and YouTube. Platforms and Interfaces The MySQL Administrator in Linux. MySQL is written in C and C++. The SQL parser uses yacc and a home-brewed lexer.[9] MySQL works on many different system platforms, including AIX, BSDi, FreeBSD, HP-UX, i5/OS, Linux, Mac OS X, NetBSD, Novell NetWare, OpenBSD, eComStation , OS/2 Warp, QNX, IRIX, Solaris, Symbian, SunOS, SCO OpenServer, SCO UnixWare, Sanos, Tru64, Windows 95, Windows 98, Windows ME, Windows NT, Windows 2000, Windows XP, and Windows Vista. A port of MySQL to OpenVMS is also available.[10] Libraries for accessing MySQL databases are available in all major programming languages with language-specific APIs. In addition, an ODBC interface called MyODBC allows additional programming languages that support the ODBC interface to communicate with a MySQL database, such as ASP or ColdFusion. The MySQL server and official libraries are mostly implemented in ANSI C/ANSI C++. To administer MySQL databases one can use the included command-line tool (commands: mysql and mysqladmin). Also downloadable from the MySQL site are GUI administration tools: MySQL Administrator and MySQL Query Browser. Both of the GUI tools are now included in one package called tools/5.0.html MySQL GUI Tools. In addition to the above-mentioned tools developed by MySQL AB, there are several other commercial and non-commercial tools available. Examples include phpMyAdmin, a free Web-based administration interface implemented in PHP, and Navicat Lite Edition, a free desktop based GUI tool. Features As of August 2007[update], MySQL offers MySQL 5.0 in two different variants: the MySQL Community Server and Enterprise Server. They have a common code base and include the following features: A broad subset of ANSI SQL 99, as well as extensions Cross-platform support Stored procedures Triggers Cursors Updatable Views True VARCHAR support INFORMATION_SCHEMA Strict mode X/Open XA distributed transaction processing (DTP) support; two phase commit as part of this, using Oracle's InnoDB engine Independent storage engines (MyISAM for read speed, InnoDB for transactions and referential integrity, MySQL Archive for storing historical data in little space) Transactions with the InnoDB, BDB and Cluster storage engines; savepoints with InnoDB SSL support Query caching Sub-SELECTs (i.e. nested SELECTs) Replication with one master per slave, many slaves per master, no automatic support for multiple masters per slave. Full-text indexing and searching using MyISAM engine Embedded database library Partial Unicode support (UTF-8 sequences longer than 3 bytes are not supported; UCS-2 encoded strings are also limited to the BMP) ACID compliance using the InnoDB, BDB and Cluster engines Shared-nothing clustering through MySQL Cluster The MySQL Enterprise Server is released once per month and the sources can be obtained either from MySQL's customer-only Enterprise site or from MySQL's Bazaar repository, both under the GPL license. The MySQL Community Server is published on an unspecified schedule under the GPL and contains all bug fixes that were shipped with the last MySQL Enterprise Server release. Binaries are no longer provided by MySQL for every release of the Community Server.[11][12] Replication support (i.e. Master-Master Replication & Master-Slave Replication) Distinguishing features The following features are implemented by MySQL but not by some other RDBMS software: Multiple storage engines, allowing you to choose the one which is most effective for each table in the application (in MySQL 5.0, storage engines must be compiled in; in MySQL 5.1, storage engines can be dynamically loaded at run time): Native storage engines (MyISAM, Falcon, Merge, Memory (heap), Federated, Archive, CSV, Blackhole, Cluster, Berkeley DB, EXAMPLE, and Maria) Partner-developed storage engines (InnoDB, solidDB, NitroEDB, BrightHouse) Community-developed storage engines (memcached, httpd, PBXT, Revision Engine) Custom storage engines Commit grouping, gathering multiple transactions from multiple connections together to increase the number of commits per second. Server compilation type There are 3 types of MySQL Server Compilations for Enterprise and Community users: Standard: The MySQL-Standard binaries are recommended for most users, and include the InnoDB storage engine. Max: (not MaxDB, which is a cooperation with SAP AG) is mysqld-max Extended MySQL Server. The MySQL-Max binaries include additional features that may not have been as extensively tested or are not required for general usage. The MySQL-Debug binaries have been compiled with extra debug information, and are not intended for production use, because the included debugging code may cause reduced performance. Beginning with MySQL 5.1, MySQL AB has stopped providing these different package variants. There will only be one MySQL server package, which includes a mysqld binary with all functionality and storage engines enabled. Instead of providing a separate debug package, a server binary with extended debugging information is also included in the standard package.[13] History Milestones in MySQL development include: MySQL was first released internally on 23 May 1995 Windows version was released on 8 January 1998 for Windows 95 and NT Version 3.23: beta from June 2000, production release January 2001 Version 4.0: beta from August 2002, production release March 2003 (unions) Version 4.1: beta from June 2004, production release October 2004 (R-trees and B-trees, subqueries, prepared statements) Version 5.0: beta from March 2005, production release October 2005 (cursors, stored procedures, triggers, views, XA transactions) Sun Microsystems acquired MySQL AB on 26 February 2008.[3] Version 5.1: production release 27 November 2008 (event scheduler, partitioning, plugin API, row-based replication, server log tables)   Future releases The MySQL 6 roadmap outlines support for: Foreign Key Additional Unicode characters utf16, utf32, and 4-byte utf8 New transactional storage engine (Falcon). Support for parallelization is also part of the roadmap for future versions.[14] Support for supplementary Unicode characters, beyond the 65,536 characters of the Basic Multilingual Plane (BMP) is announced for MySQL 6.0. Foreign key support for all storage engines is targeted for release in MySQL 6.1 (although it has been present since version 3.23.44 for InnoDB). A new storage engine is also in the works, called Falcon. A preview of Falcon is already available on MySQL's website. Support and licensing Via MySQL Enterprise MySQL AB offers support itself, including a 24/7 service with 30-minute response time, the support team has direct access to the developers as necessary to handle problems. In addition it hosts forums and mailing lists, employees and other users are often available in several IRC channels providing assistance. Buyers of MySQL Enterprise have access to binaries and software that is certified for their particular operating system, and access to monthly binary updates with the latest bug fixes. Several levels of Enterprise membership are available, with varying response times and features ranging from how to and emergency support through server performance tuning and system architecture advice. The MySQL Network Monitoring and Advisory Service monitoring tool for database servers is available only to MySQL Enterprise customers. MySQL Server is available as free software under the GNU General Public License (GPL), and the MySQL Enterprise subscriptions include a GPL version of the server, with a traditional proprietary version available on request at no additional cost for cases where the intended use is incompatible with the GPL.[15] Both the MySQL server software itself and the client libraries are distributed under a dual-licensing format. Users may choose the GPL,[16] which MySQL has extended with a FLOSS License Exception. It allows Software licensed under other OSI-compliant Open Source licenses, which are not compatible to the GPL, to link against the MySQL client libraries.[17] Customers that do not wish to be bound to the terms of the GPL may choose to purchase a proprietary license.[18] Like many open-source programs, the name "MySQL" is trademarked and may only be used with the trademark holder's permission. Some users have independently continued to develop earlier versions of the client libraries, which was distributed under the less-restrictive GNU Lesser General Public License (LGPL).[19] Issues There has been some controversy regarding the distribution of GPL licensed MySQL library files with other open source applications. The biggest controversy arose with PHP, which has a license incompatible with the GPL. This was later resolved when MySQL created a license exception that explicitly allows the inclusion of the MySQL client library in open source projects that are licensed under a number of OSI-compliant Open Source licenses, including the PHP License.[20] In September 2005, MySQL AB and SCO forged a partnership for "joint certification, marketing, sales, training and business development work for a commercial version of the database for SCO's new OpenServer 6 version of Unix". SCO raised controversy beginning in 2003 with a number of high-profile lawsuits related to the Linux Operating System. Various MySQL employees expressed that the company was committed to serving its end users, regardless of their operating system choice, that the company would leave it to the courts to resolve the SCO licensing controversy, and that other common open source databases have also been ported to, and support, SCO OpenServer. In October 2005, Oracle Corporation acquired Innobase OY, the Finnish company that developed the InnoDB storage engine that allows MySQL to provide such functionality as transactions and foreign keys. A press release by Oracle that was issued after the acquisition,[21] mentioned that the contracts that make the company's software available to MySQL AB would be due for renewal (and presumably renegotiation) some time in 2006. During the MySQL Users Conference in April 2006, MySQL issued a press release which confirmed that MySQL and Innobase OY agreed to a multi-year extension of their licensing agreement.[22] In February 2006, Oracle Corporation acquired Sleepycat Software,[23] makers of the Berkeley DB, a database engine onto which another MySQL storage engine was built. Criticism MySQL recently (2008) released version 5.1 with 20 known crashing and wrong result bugs in addition to the 35 present in version 5.0.[24] Critical bugs sometimes do not get fixed for long periods of time.[25][26] An example is a bug with status critical existing since 2003.[27] MySQL shows poor performance when used for Data Warehousing; this is partly due to inability to utilize multiple CPU cores for processing a single query.[28] The developer of the Federated Storage Engine states that "The Federated Storage Engine is a proof-of-concept storage engine",[29] though it was included and turned on by default in the main distributions of MySQL version 5.0. Some of the short-comings are documented in the "MySQL Federated Tables: The Missing Manual". MySQL's divergence from the SQL standard regarding the treatment of NULL values and default values has been criticized. Its handling of dates in versions prior to 5.0 allows storing a date with a day beyond the last day of a month with fewer than 31 days, and arithmetic operations are vulnerable to either integer overflow or floating point truncation.[30] Since version 5 of the server, the treatment of illegal values varies according to use of the "SQL Mode" set in the server, which is by default set to the unusually tolerant state that critics dislike.[31] When the beta version of MySQL 5.0 was released in March 2005, David Axmark, a co-founder of MySQL, said that "People have been criticizing MySQL since we started for not having stored procedures, triggers and views," and "We're fixing 10 years of criticism in one release."[32] MySQL 5.0's 13 October build 5.0.15 was released for production use on 24 October 2005, after more than two million downloads in the 5.0 beta cycle.