oracle触发器实现出入库

income{ 
id number; 
pay_amount number;(入库金额字段) 
} 
outlay{ 
id number; 
outlay_amount number;(出库金额字段) 
} 
balance 
{ 
id number; 
balance number;(余额字段) 
} 
 
下面分别在入库和出库表中建立触发器 
入库表（income）: 
 代码如下:

CREATE TRIGGER "AA"."TRI_ADD" AFTER 
INSERT 
OR DELETE ON "INCOME" FOR EACH ROW begin 
if deleting then 
update balance set balance = nvl(balance,0) - :old.pay_amount; 
elsif updating then 
update balance set balance = nvl(balance,0) - :old.pay_amount + :new.pay_amount; 
else 
update balance set balance = nvl(balance,0) + :new.pay_amount; 
end if; 
end; 
 
出库表(outlay)： 
 代码如下:

CREATE TRIGGER "AA"."TRI_CUT" AFTER 
INSERT 
OR DELETE 
OR UPDATE ON "OUTLAY" FOR EACH ROW begin 
if deleting then 
update balance set balance = nvl(balance,0) + :old.outlay_amount; 
elsif updating then 
update balance set balance = nvl(balance,0) + :old.outlay_amount - :new.outlay_amount; 
else 
update balance set balance = nvl(balance,0) - :new.outlay_amount; 
end if; 
end; 
 
下面我解释一下 
oracle触发器，触发事件分为插入，删除，更新列三种事件，分别对应inserting /deleting/updating关键字 
可以用if语句分别实现 
 代码如下:

if inserting then 
----- 
elsif updating then 
----- 
elsif deleting then 
------ 
end if; 
 
NVL(eExpression1, eExpression2) 
如果 eExpression1 的计算