Ubuntu Unleashed 2013 Edition: Covering 12.10 and 13.04, Eighth Edition

Procedural Languages and Triggers

A procedural language is an external programming language that you can use to write functions and procedures. With a procedural language, you can do things that aren’t supported by simple SQL. A trigger enables you to define an event that invokes the external function or procedure you have written. For example, you can use a trigger to cause an exception if an INSERT statement containing an unexpected or out-of-range value for a column is given.

For example, in the CD tracking database, you could use a trigger to cause an exception if a user enters data that does not make sense. PostgreSQL has a procedural language called PL/pgSQL. Although MySQL has support for a limited number of built-in procedures and triggers, ...