触发器

CREATE OR REPLACE TRIGGER check_emp
               BEFORE update OR insert OR delete ON emp
           --BEFORE 和AFTER指出触发器的触发时序分别为前触发和后触发方式
         REFERENCING new AS nn  old AS oo
         FOR EACH ROW
         WHEN (nn.sal > 2000)  --判定条件
     BEGIN
         IF INSERTING THEN
            dbms_output.put_line('THE OPERATION IS INSERT');
        --增加INSERT  INTO EMP values(7554,'HIHJ','RTUT',1202,SYSDATE,2700,200,20,null,null

         ELSIF UPDATING THEN
             dbms_output.put_line('THE OPERATION IS UPDATE');  
        --改  UPDATE EMP SET SAL=6000 WHERE EMPNO=7840
         ELSIF DELETING THEN
             dbms_output.put_line('THE OPERATION IS DELETE');
        --删操作  delete emp where  empno=7555
         ELSE
             dbms_output.put_line('OTHERS OPERATION');
         END IF;
     END;