15.1. Overview

A trigger is an SPL code block that is given a name, associated with a table, and stored in the database. When certain events occur on the table the SPL code block is executed. The trigger is said to be fired when the code block is executed.

The event that causes a trigger to fire can be any combination of an insert, update, or deletion carried out on the table, either directly or indirectly. If the table is the object of a SQL INSERT, UPDATE, or DELETE command the trigger is directly fired assuming that the corresponding insert, update, or deletion event is defined as a triggering event. The events that fire the trigger are defined in the CREATE TRIGGER command.

A trigger can be fired indirectly if a triggering event occurs on the table as a result of an event initiated on another table. For example, if a trigger is defined on a table containing a foreign key defined with the ON DELETE CASCADE clause and a row in the parent table is deleted, all children of the parent would be deleted as well. If deletion is a triggering event on the child table, deletion of the children will cause the trigger to fire.