Question

我有一个带有users表，credit_purchase表和credit_spend表的应用程序。我试图获得用户目前拥有的信用额度。

信用表如下：

credit_purchase

+----+---------+-------+---------------------+
| id | user_id | coins | timestamp           |
+----+---------+-------+---------------------+

credit_spend

+----+---------+-------+---------------------+
| id | user_id | coins | timestamp           |
+----+---------+-------+---------------------+

我要做的是为每个用户选择SUM（credit_purchase.coins） - SUM（credit_spend.coins）。现在我有这样的事情：

SELECT users.*, COALESCE(SUM(credit_purchase.coins) - SUM(credit_spend.coins), 0) 
FROM users 
LEFT JOIN credit_purchase ON users.id = credit_purchase.user_id 
LEFT JOIN credit_spend ON users.id = credit_spend.user_id 
GROUP BY users.id

但是，结果不是正确的数字。这似乎是正确地对购买进行调整，但是将SUM与花费乘以购买数量。

我做错了什么？

谢谢！

Answer 1

试试这个：

SELECT  users.*, 
        COALESCE(SUM(credit_purchase.coins) - SUM(credit_spend.coins), 0) 
FROM    users 
            LEFT JOIN credit_purchase
                    ON users.id = credit_purchase.user_id 
            LEFT JOIN credit_spend 
                    ON users.id = credit_spend.user_id 
GROUP BY users.id

为每个用户选择两个表的SUM

1 个答案: