CREATE OR REPLACE TRIGGER trig_sal
    AFTER UPDATE OF empsal ON salary_records  --在更新 emp_sal 列之后激活触发器
    …

        …
    FOR EACH ROW
    WHEN (NEW.empsal>OLD.empsal)    --只有在WHEN子句中的条件得到满足时，才激活trig_sal 触发器
    DECLARE
    Sal_diff NUMBER;
    …    

        …
    BEGIN
      sal_diff:=:NEW.empsal-:OLD.empsal;    --如果WHEN子句中的条件得到满足，将执行BEGIN 块中的代码
      DBMS_OUTPUT.PUT_LINE(‘工资差额：’sal_diff);
    END;

CREATE OR REPLACE TRIGGER aiu_itemfile
AFTER INSERT
ON itemfile
FOR EACH ROW
BEGIN
  IF (:NEW.qty_hand = 0) THEN
    DBMS_OUTPUT.PUT_LINE(‘警告：已插入记录，但数量为零‘);
  ELSE
    DBMS_OUTPUT.PUT_LINE(‘已插入记录‘);
  END IF;
END;

select * from all_triggers where table_name =upper(‘tbname‘)   

CREATE OR REPLACE TRIGGER TR_SEC_EMP
BEFOR INSERT  OR UPDATE OR DELETE ON EMP2
BEGIN 
 IF TO_CHAR(SYSDATE,’DY’, ‘nls_date_language=AMERICAN’) IN (‘SAT’, ‘SUN’) THEN 
RAISE_APPLICATION_ERROR(-20002,’禁止修改数据！’);
END IF;
END;

create or replace trigger guo_trigger----创建触发器 
before update on emp2 ----指明触发器时机 
for each row ----行触发器标识 
when (new.sal<old.sal ) ----触发条件 
begin 
raise_application_error(-20500,‘不能给员工减少工资‘); 
end; 

CREATE TABLE TEST_TRG
          (ID NUMBER, NAME VARCHAR2(20));
CREATE SEQUENCE SEQ_TEST;

CREATE OR REPLACE TRIGGER BI_TEST_TRG
　　BEFORE INSERT OR UPDATE OF ID
　　ON TEST_TRG
　　FOR EACH ROW
BEGIN
--函数UPDATING, DELETING判断触发器是由哪个操作触发的 
     IF INSERTING THEN SELECT SEQ_TEST.NEXTVAL INTO :NEW.ID FROM DUAL;
     ELSE
       RAISE_APPLICATION_ERROR(-20020, ‘不允许更新ID值！‘);
     END IF;
END;

CREATE OR REPLACE TIGGER TR_SAL_BACK AFFTER UPDATE OF SAL ON EMP2 FOR EACH ROW 
DECLARE 
　　V_TEM INT ;
BEGIN 
　　SELECT COUNT(*) INTO V_TEMP FROM NEW_BACK WHERE ENAME =:OLD.ENAME;
　　IF V_TEMP =0 THEN 
　　　　INSERT INTO NEW_BACK VALUES (:OLD.ENAME,:OLD.SAL, :NEW.SAL,SYSDATE);
　　ELSE 
　　　　UPDATE NEW_BACK VALUES  SET OLDSAL=:OLDSAL, NEWSAL=:NEW.SAL,TIME=SYSDATE WHERE NAME=:OLD.ENAME;
　　END IF; 
END;

CREATE TABLE emp_his AS SELECT * FROM EMP WHERE 1=2; 

CREATE OR REPLACE TRIGGER tr_del_emp BEFORE 
DELETE --指定触发时机为删除操作前触发
   ON scott.emp 
   FOR EACH ROW   --说明创建的是行级触发器 
BEGIN
   --将修改前数据插入到日志记录表 del_emp ,以供监督使用。
   INSERT INTO emp_his(deptno , empno, ename , job ,mgr , sal , comm , hiredate )
       VALUES( :old.deptno, :old.empno, :old.ename , :old.job,:old.mgr, :old.sal, :old.comm, :old.hiredate );
END;

DELETE emp WHERE empno=7788;
DROP TABLE emp_his;
DROP TRIGGER del_emp;

CREATE OR REPLACE TRIGGER trgdemo
   AFTER INSERT OR UPDATE OR DELETE
   ON order_master
BEGIN
   IF UPDATING THEN
     DBMS_OUTPUT.PUT_LINE(‘已更新 ORDER_MASTER 中的数据‘);
   ELSIF DELETING THEN
     DBMS_OUTPUT.PUT_LINE(‘已删除 ORDER_MASTER 中的数据‘);
   ELSIF INSERTING THEN
     DBMS_OUTPUT.PUT_LINE(‘已在 ORDER_MASTER 中插入数据‘);
   END IF;
END;

CREATE OR REPLACE TRIGGER upd_ord_view
　　INSTEAD OF UPDATE ON ord_view
　　FOR EACH ROW
BEGIN
　　UPDATE order_master
　　SET vencode=:NEW.vencode 
　　　　WHERE orderno = :NEW.orderno;
　　DBMS_OUTPUT.PUT_LINE(‘已激活触发器‘);
END;

CREATE TABLE dropped_obj 
(
　　obj_name VARCHAR2(30),
　　obj_type VARCHAR2(20),
　　drop_date DATE
);


CREATE OR REPLACE TRIGGER log_drop_obj
　　AFTER DROP ON SCHEMA
BEGIN
　　INSERT INTO dropped_obj
　　VALUES( ORA_DICT_OBJ_NAME, ORA_DICT_OBJ_TYPE, SYSDATE);
END;

ALTER TRIGGER aiu_itemfile DISABLE;

ALTER TRIGGER aiu_itemfile ENABLE;

DROP TRIGGER aiu_itemfile;

SELECT TRIGGER_NAME FROM USER_TRIGGERS
WHERE TABLE_NAME=‘EMP‘;



SELECT TRIGGER_TYPE, TRIGGERING_EVENT, WHEN_CLAUSE
FROM USER_TRIGGERS
WHERE TRIGGER_NAME = ‘BIU_EMP_DEPTNO‘;