MySQL
MySQL is a multithreaded, multi-user, SQL (Structured Query Language)
relational database server (RDBS). MySQL is available either under the GNU General Public License (GPL) or under other
licenses when the GPL is inapplicable to the intended use.
Unlike projects such as Apache, MySQL is owned and sponsored
by a single for-profit firm, MySQL AB. The MySQL trademark and copyright are owned
by the Swedish company MySQL AB. The
company develops and maintains the system, selling support and service
contracts, as well as commercially-licensed copies of MySQL, and employing people all over the world who communicate over the internet. Two Swedes and a Finn founded MySQL
AB: David Axmark, Allan Larsson and Michael "Monty" Widenius.
Despite the widespread pronunciation of "SQL" as "sequel",
professionals generally pronounce "MySQL" as "my ess-que-ell", not
"my-sequel" [1] (http://dev.mysql.com/doc/mysql/en/What-is.html#IDX25).
Platforms
MySQL works on many different platforms—including AIX, BSDi, FreeBSD, HP-UX, Linux, Mac OS X, NetBSD,
Netware, OpenBSD, OS/2 Warp, QNX, SGI IRIX, Solaris, SunOS, SCO OpenServer, SCO UnixWare,
Tru64, Windows 95, Windows 98, Windows
NT, Windows 2000, Windows
XP, and more recent versions of Windows. A port of MySQL to
OpenVMS is available here (http://www.pi-net.dyndns.org/anonymous/kits/).
Programming languages
Programming languages which can access MySQL databases
include: C, C++, Eiffel, Smalltalk, Java (with a native Java driver implementation), Lisp, Perl,
PHP, Python, Ruby,
and Tcl; each of these using a specific API. An ODBC interface called MyODBC allows additional programming languages that support the ODBC interface
to communicate with a MySQL database. MySQL uses ANSI C as its "native" language.
Uses
MySQL is popular for web applications like BambooWeb and PHP-Nuke and acts as the
database component of LAMP. The popularity as a web application is closely tied to the
popularity of PHP, which is often combined with MySQL and nicknamed the Dynamic Duo.
It is easy to find many references that combine the two from books (PHP and MySQL for Dummies, PHP and MySQL Bible,
Beginning PHP and MySQL....) to websites. The implication in many books is that MySQL is easier to learn and use than many
other database applications. An example from the Dummies book is that you can quit MySQL with an obvious command of either
exit or quit.
The latest production version
As of 2004, MySQL offers production version 4.1.7. It includes the following
features:
- A broad subset of ANSI SQL 99, as well as extensions
- Cross-platform support
- Independent storage engines (MyISAM for read speed, InnoDB for transactions and referential integrity)
- Transactions, including savepoints
- SSL support
- Query caching
- Sub-SELECTs (or nested SELECTs)
- Replication with one master per slave, many slaves per master
- Full-text indexing and searching using MyISAM engine
- Embedded database library
- Full Unicode support
- ACID compliance using InnoDB engine
- Shared-nothing clustering through MySQL Cluster
It does not include the following features:
Future releases
MySQL 5.0 contains support for the following features:
- Stored procedures
- Views
- Cursors
- True VARCHAR support
- Easier GIS access
- Triggers
MySQL 5.1 will contain support for:
- Online backup for all storage engines
- Foreign key support for all storage engines
- Fail-safe replication
- Column-level constraints
Criticisms of MySQL
Early versions of MySQL included few standard RDBMS features, and the current production version still lacks many properties
found in other SQL RDBMSs. This has led some database experts, such as Chris Date and Fabian Pascal, to criticize
MySQL as falling short of being an RDBMS. [2] (http://www.dbdebunk.com/)
Many of the early criticisms have been remedied in later versions of the software, including the lack of transactions and
relational integrity constraints. These are features necessary to support the "ACID
properties" for relational databases, which allow the DBMS to ensure that client applications cannot interfere with one another
or insert inconsistent values. [3] (http://www.service-architecture.com/database/articles/acid_properties.html) Other criticisms
include MySQL's divergence from the SQL standard on the subject of treatment of NULL values and default values. Its handling of
dates allowed invalid dates to be stored, and arithmetic operations are vulnerable to either integer overflow or floating point
truncation. [4] (http://sql-info.de/mysql/gotchas.html)
Earlier versions of the MySQL manual included claims that certain essential missing features were useless or even harmful, and
that users were better off without them. One section, entitled "Reasons NOT to use Foreign Keys constraints" (sic) advised users
that relational-integrity checking was difficult to use and complicated a database application, and that its only useful purpose
was to allow client software to diagram the relationships between database tables. [5] (http://sunsite.univie.ac.at/textbooks/mysql/manual.html#Broken_Foreign_KEY) Another section claimed
that a DBMS lacking transactions can provide as reliable of data-integrity assurances as one supporting them -- conflating the
issue of transactional integrity with that of saving data when the database server loses power. [6] (http://sunsite.univie.ac.at/textbooks/mysql/manual.html#IDX340) Since these claims contradicted
basic principles of relational database design, they caused
MySQL to be ridiculed by some database experts. Right or wrong, these claims have since been removed in more recent versions of
the manual. MySQL today supports the previously-dismissed features of relational integrity checking and transactions in an effort
to meet the broadest needs, and facilitate migration efforts.
Critics find MySQL's popularity surprising in the light of the existence of other open-source database projects with
comparable performance and in closer compliance to the SQL standards. MySQL advocates reply that the program serves its purpose
for its users, who are willing to accept the program's limitations (which decrease with every major revision) in exchange for
speed, simplicity, and rapid development.
Some users have also criticized MySQL AB's position on the licensing of the software.
Licensing
Both the MySQL server software itself and the client libraries are distributed under a dual-licensing format. Users may choose
GNU General Public
License [7] (http://www.mysql.com/products/licensing/opensource-license.html), or they may choose a commercial
license.
Some users have independently continued to develop an earlier version of the client libraries, which was distributed under the
less-restrictive Lesser General Public
License. [8] (http://packages.debian.org/testing/libs/libmysqlclient10)
See also
Other SQL database servers
External links
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