Database Triggers

A trigger is PL/SQL code block attached and executed by an event which occurs to a database table. Triggers are implicitly invoked by DML commands. Triggers are stored as text and compiled at execute time, because of this it is wise not to include much code in them but to call out to previously stored procedures or packages as this will greatly improve performance. You may not use COMMIT, ROLLBACK and SAVEPOINT statements within trigger blocks. Remember that triggers may be executed thousands of times for a large update – they can seriously affect SQL execution performance

Triggers may be called BEFORE or AFTER the following events :-

INSERT, UPDATE and DELETE.

Triggers may be STATEMENT or ROW types. STATEMENT triggers fire BEFORE or AFTER the execution of the statement that caused the trigger to fire. ROW triggers fire BEFORE or AFTER any affected row is processed.

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