Use

SQL Trigger

CREATE TRIGGER SalaryTrigger
AFTER UPDATE OF salary ON MovieExec
REFERENCING
	OLD ROW AS OldTuple,
	NEW ROW AS NewTuple
FOR EACH ROW
WHEN (OldTuple.salary > NewTuple.salary)
	UPDATE MovieExec
	SET salary = OldTuple.salary
	WHERE execID = NewTuple.execID