Application Development Guide

Overview of a Trigger

When you create a trigger, you associate it with a table. This table is called the subject table of the trigger. The term update operation refers to any change in the state of the subject table. An update operation is initiated by:

• an INSERT statement
• an UPDATE statement, or a referential constraint which performs an UPDATE
• a DELETE statement, or a referential constraint which performs a DELETE

You must associate each trigger with one of these three types of update operations. The association is called the trigger event for that particular trigger.

You must also define the action, called the triggered action, that the trigger performs when its trigger event occurs. The triggered action consists of one or more SQL statements which can execute either before or after the database manager performs the trigger event. Once a trigger event occurs, the database manager determines the set of rows in the subject table that the update operation affects and executes the trigger.

When you create a trigger, you declare the following attributes and behavior:

• The name of the trigger.
• The name of the subject table.
• The trigger activation time (BEFORE or AFTER the update operation executes).
• The trigger event (INSERT, DELETE, or UPDATE).
• The old values transition variable, if any.
• The new values transition variable, if any.
• The old values transition table, if any.
• The new values transition table, if any.
• The granularity (FOR EACH STATEMENT or FOR EACH ROW).
• The triggered action of the trigger (including a triggered action condition and triggered SQL statement(s)).
• If the trigger event is UPDATE, then the trigger column list for the trigger event of the trigger, as well as an indication of whether the trigger column list was explicit or implicit.
• The trigger creation timestamp.
• The current function path.

For more information on the CREATE TRIGGER statement, refer to the SQL Reference.