触发器：对指定表中的某一列数据进行修改触发

create or replace trigger tr_xzcz
before update  or delete on STU
for each row 
begin 
        dbms_output.put_line('执行。。。。');
        IF :OLD.SDEPT = '12计算机' THEN
            IF UPDATING THEN
                IF :NEW.SAGE <> :OLD.SAGE then
                    dbms_output.put_line('本班级学生年龄不能修改');
                END IF;
            END IF;
            IF DELETING then
                dbms_output.put_line('数据被删除');
            END IF; 
        END IF;     
END;
DELETE FROM STU WHERE SNO = '120005';