In a DELETE or UPDATE trigger, the letters “OLD” or an OLD correlation-name must be prepended to a column name to reference a column in the row of data prior to the update or delete operation.
In an INSERT or UPDATE trigger, the letters “NEW” or a NEW correlation-name must be prepended to a column name to reference a column in the row about to be inserted or updated.
Triggers are executed either before or after an UPDATE,
INSERT, or
DELETE statement is executed, depending on the type of trigger.