一个很好的触发器例子（case when）

CREATE OR REPLACE TRIGGER TR_CGD1
BEFORE UPDATE OR INSERT OR DELETE ON BB_MJ_CGD1_TB
FOR EACH ROW
DECLARE

V_COUNT NUMBER;
BEGIN
CASE
WHEN UPDATING OR INSERTING THEN
IF :NEW.DJZT = ‘结束‘ THEN
:NEW.DJZT := ‘结束‘;
ELSE
SELECT COUNT(*)
INTO V_COUNT
FROM BB_MJ_KCRKD2_TB RKD2
WHERE CGD2ID IN
(SELECT ID FROM BB_MJ_CGD2_TB WHERE CGD1ID = :NEW.ID);
END IF;
WHEN DELETING THEN
SELECT COUNT(*)
INTO V_COUNT
FROM BB_MJ_KCRKD2_TB RKD2
WHERE CGD2ID IN
(SELECT ID FROM BB_MJ_CGD2_TB WHERE CGD1ID = :OLD.ID);
END CASE;
IF V_COUNT > 0 THEN
RAISE_APPLICATION_ERROR(-20002, ‘订单已入库，不可修改‘);
END IF;
END;