mysql - 如何增加或减少另一个表的值？

Question

我有两张 table - 袋子和市场。

此时bags表中有如下数据:

如果我从市场表中添加数据，则表袋中的数量列将根据市场表中输入的数量而减少。而总价一栏会计算total_qty(市场)*price(袋数)

Answer 1

根据我的理解，我建议这个概念使用触发器，

DELIMITER $$
 CREATE TRIGGER trg_insert
 AFTER INSERT ON market

 begin
 update bags set qty = ((select qty from bags where id=1)-(select 
 market.total_qty from market where 
 id=1) ))
 ,price = ((select price from basgs where id=1)-(select market.total_prc 
  from market where 
 market.id=1)))
 where bags.id = 1;
  END$$
 DELIMITER $$

Now i am using with static values which you are provided, Try this code.