Orcale 级联更新删除功能

 CREATE OR REPLACE TRIGGER tre_del_update
 BEFORE DELETE OR UPDATE ON dept FOR EACH ROW
 BEGIN
 IF DELETING THEN
    DELETE FROM emp WHERE deptno=:old.deptno;
 ELSIF updating THEN
    UPDATE emp SET deptno=:NEW.deptno WHERE deptno=:OLD.deptno;
 END IF;
 END tre_del_update;