CREATE OR REPLACE TRIGGER TRG_LATE_RETURN
BEFORE UPDATE
ON DETAILRENTAL
FOR EACH ROW
WHEN (OLD.due_date <> NEW.due_date OR OLD.RETURN_DATE <> NEW.RETURN_DATE)
DECLARE
oldRetDate DETAILRENTAL.RETURN_DATE%TYPE :=old.RETURN_DATE;
newRetDate DETAILRENTAL.RETURN_DATE%TYPE :=NEW.RETURN_DATE;
oldDueDate DETAILRENTAL.due_date%TYPE := old.due_date;
newDueDate DETAILRENTAL.due_date%TYPE := NEW.due_date;
BEGIN
IF oldDueDate <> newDueDate THEN
   DETAILRENTAL.DAYS_LATE := newRetDate - newDueDate;
ELSE
   IF newRetDate = NULL THEN
      DETAILRENTAL.DAYS_LATE := NULL;
   ELSIF oldRetDate <= :oldDueDate  THEN
      DETAILRENTAL.DAYS_LATE := 0;
   ELSIF newRetDate > :oldDueDate THEN
     DETAILRENTAL.DAYS_LATE := newRetDate - newDueDate;
   END IF;
END IF;
EXCEPTION
  WHEN OTHERS THEN
   DBMS_OUTPUT.PUT_LINE ('Unexpected error occured');
END;
/
show errors;