MYSQL SUM数量加入

Question

我的SQL查询有问题。当我使用多个JOIN时，结果是错误的。

SELECT name, stock,SUM(order_items.qty),
SUM(shipping_items.qty) FROM shipping_items

JOIN mnm_products 
ON mnm_products.id = shipping_items.product_id

JOIN order_items
ON mnm_products.id = order_items.product_id

GROUP BY mnm_products.id

当我只使用

时

SELECT name, stock,
SUM(shipping_items.qty) FROM shipping_items

JOIN mnm_products 
ON mnm_products.id = shipping_items.product_id
GROUP BY mnm_products.id

是对的。但是当我使用2个连接时。两者的结果是一样的。 有人可以帮助我吗？

Answer 1

相关子查询可能最好：

select p.*,
       (select sum(si.qty)
        from shipping_items si
        where si.product_id = p.id
       ) as shipping_items,
       (select sum(oi.qty)
        from order_items oi
        where oi.product_id = p.id
       ) as order_items
from mnm_products p;