Question

如果order_status从0变为1或2，我试图制作一个必须进行减法的触发器。更新的order_status行中的数量值应该从另一个表中的quantity_in_stock中减去。这是我尝试过的，但它不适合我。

begin
   DECLARE orderQuantity INT(11);
   if old.order_status = 0 and new.order_status != 0 then 
   select quantity into orderQuantity from `order` where id=new.id;
   update product_in_stock
   set quantity_in_stock = sum(quantity_in_stock - orderQuantity)
   where id=1;
   end if;
end

Answer 1

除非您已经定义了自己的sum功能，否则您的使用方式是错误的

而不是set quantity_in_stock = sum(quantity_in_stock - orderQuantity)

应为set quantity_in_stock = sum(quantity_in_stock) - sum(orderQuantity)

但同样，你不能直接使用聚合函数，除非它在having子句中。

你可以做什么，declare two variable -> fetch the sum separately and store them to variable -> use them喜欢

DECLARE sum_quantity_in_stock INT(11);
DECLARE sum_orderQuantity INT(11);

select sum(quantity_in_stock) into sum_quantity_in_stock from sometable;
select sum(orderQuantity) into sum_orderQuantity from sometable;


set quantity_in_stock = sum_quantity_in_stock - sum_orderQuantity

Mysql触发器在2个表中进行计算？

1 个答案: