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What is it?
Structured Query Language (SQL) is used to interrogate and process data in a relational database. It was developed by IBM for use on mainframes. SQL commands can work interactively with a database or be embedded in a programming language.
Relational database management systems (RDBMS) may be the next field to go open source, with fully SQL-compliant Ansi-(American National Standards Institute) approved open source databases threatening to enter the mainstream. The three leading choices are MySQL, PostgreSQL and Interbase.
In November 2000, US space agency Nasa replaced Oracle with MySQL for a single non-critical application, the Nasa Acquisition Internet Service (NAIS). But the news should alarm proprietary database suppliers. The NAIS project leader reports an increase in performance and no problems.
Nasa says the switch to open source was driven by cost.
Where did it originate?
SQL was developed by IBM in the 1970s. It is both an Ansi and ISO standard.
What makes it special?
SQL is the standard relational database language. All relational database products - Oracle, DB2,
SQL Server and the rest - are based on it. SQL is usually used within a programming language such as C, Cobol or Java.
"From one release to the next, Postgres [one of the organisations offering open source RDBMS software] adds major features within a matter of months, equivalent to upgrades that commercial software companies take years to introduce," says Ned Lilly, vice-president of open source development at software supplier Great Bridge.
"The unprecedented rate of revision stems from hundreds of loyal and enthusiastic developers and users who brainstorm fixes and test the latest tweaks, quickly reporting results from all kinds of applications, configurations and platforms."
The simplicity of the open source licensing appeals to many businesses resentful of the charges that the big suppliers impose.
How difficult is it?
You can study SQL on its own - QA Training runs a two-day course, for example - but you would normally learn it as part of a supplier's database programming course, such as Oracle's PL/SQL or Microsoft's Transact-SQL. With SQL experience, you can train in an open source database in two to three days.
Where is it used?
Like Linux, open source databases are being introduced to larger organisations semi-officially by techies, but there are some commercial users. Yahoo Finance uses MySQL, and Motorola includes it in its developers' toolkit for the Iden handset network system.
What does it run on?
Interbase comes from Borland, which turned it from a proprietary to an open source RDBMS under the Mozilla public license.
PostgreSQL was created by adding SQL to Postgres, which in turn was evolved from Ingres by Michael Stonebraker at Berkeley.
MySQL has widespread backing. One distributor is NuSphere, owned by the embedded database market leader, Progress Software. MySQL is also included in Red Hat Linux 7.
Open source with something you find in a relish tray.
Few people know that
There is an open source site for Oracle's PL/SQL, at www.plnet.sourceforge.net.
What's coming up?
Open source databases certified for mainstream operating systems including Windows and Solaris.
Although there are various SQL courses, a lot of open source training, like the software, is available free online.