ABSTRACT
A trigger is a PL/SQL procedure that executes when a table-modifying event (insert, delete, or update) occurs. Triggers may be fired for each row affected (FOR ANY ROW [WHEN] ...), or may be fired at the statement level for an insert, update, or delete operation. Triggers may be fired before or after an event (a triggering action) takes place. There are therefore 12 categories of triggers (before/after, row/statement, update/insert/delete):
Before update row-level Before update statement-level After update row-level After update statement-level ...plus four for insert and four for delete
A trigger’s category is defined by the type of triggering transaction (before update, after update, before insert, etc.), and by the level at which the trigger is executed (statement or row). The execution of a trigger may often be transparent to the user.
