Chapter 3. An Introduction to SQL

Structured Query Language (SQL) is a database query language that was adopted as an industry standard in 1986. A major revision of the SQL standard, SQL2, was released in 1992. Its successor, SQL3, also contains object-oriented components . Currently, ANSI SQL92 is the most important standard.

This language enables you to pose complex questions to a database. It also provides a means of modifying databases. SQL is widely used. Many databases support SQL, which means that if you learn how to use SQL, you can apply this knowledge to MS SQL Server, DB2, Oracle, PostgreSQL, and countless other databases. SQL works with relational databases, which store data in objects. An object can be a table, for example. A database is a collection of tables and functions. A table consists of a list of records; each record ( row ) in a table has the same structure and each has a fixed number of fields ( columns ) of a given type. SQL can be used to communicate with a database and its components.

Every database has a slightly different version of SQL implemented, so it can sometimes be very hard to port applications from one database to another. For that reason, ANSI SQL92 has been developed. ANSI SQL92 is a standard that should be understood by every database supporting SQL. Unfortunately, many commercial database developers don't implement fully ANSI SQL92 “compatible SQL engines in their databases.

PostgreSQL developers are working hard to make PostgreSQL 100% ANSI SQL “compatible. Therefore, PostgreSQL applications are portable and easy to understand.

For further information about the ANSI SQL92 standard or any other ANSI standard, check out http://www.ansi.org.