A trigger is a set of actions that are run automatically when a specified change operation is performed on a specified table or view. The change operation can be an SQL INSERT, UPDATE, or DELETE statement, or an insert, update, or delete high-level language statement in an application program. Triggers are useful for tasks such as enforcing business rules, validating input data, and keeping an audit trail.
Triggers can be defined as SQL or external.
For an external trigger, the CRTPFTRG CL command is used. The program containing the set of trigger actions can be defined in any supported high level language. External triggers can be insert, update, delete, or read triggers.
For an SQL trigger, the CREATE TRIGGER statement is used. The trigger program is defined entirely using SQL. SQL triggers can be insert, update, or delete triggers.
Once a trigger is associated with a table or view, the
trigger support calls the trigger program whenever a change operation is initiated
against the table or view, or any logical file or view created over the table
or view. SQL triggers and external triggers can be defined for the same table.
Only SQL triggers can be defined for a view. Up to 200 triggers can be defined
for a single table or view.
Each change operation for a table can call a trigger before
or after the change operation occurs. Additionally, you can add a read trigger
that is called every time the table is accessed. Thus, a table can be associated
with many types of triggers.
- Before delete trigger
- Before insert trigger
- Before update trigger
- After delete trigger
- After insert trigger
- After update trigger
- Read-only trigger (external trigger only)
Each change operation for a view can call an instead of
trigger which will perform some set of actions instead of the
insert, update, or delete. A view can be associated with an:
- Instead of delete trigger
- Instead of insert trigger
- Instead of update trigger