SQL (Structured Query Language) is a query language for relational
databases. The roots of SQL go back to SQUARE, a more mathematical oriented
language and SEQUEL, a predecessor of SQL from the seventies. There exist
different standards (ISO and ANSI) of SQL, but the most common one is SQL-92.
The latest standard SQL-99 (or SQL3) even includes XML. In the following Units
we will give a simple overview of the most important SQL functions.
This lesson is geared to the SQL-99 standard
(GULUTZAN et al. 1999). However,
this standard is not implemented by all database systems constantly. For example,
some commands are named differently or their syntax is constructed differently. For
this reason, SQL commands from this lesson might not work in certain systems. If
you encounter problems, please check in the respective user manuals whether or not
the command is supported at all, whether it is named, or constructed differently.
Most database systems also go beyond the standard. However, caution is advised with
these SQL extensions since they can vary considerably from system to system.