Question

我有四个mysql表client，transaction，other_loan和payment。我想从sum和{{中获取表load_amount的{{1}}和additional到表transaction的{{1}}和sum的{{1}} 1}}到表amount中other_loan的{{1}}中。我该如何实现？

我想要的结果：

subtract

我的桌子：交易

sum

表：other_loan

payment_amount

表格：付款

payment

表：客户

>  ID | Name     |  Amount
>  1  | Robin    | 8718  
>  2  | Reynaldo | 21
>  3  | Leomar   | 0

Answer 1

由于您有多个交易，其他每个客户的贷款额和还款额，因此您无法对表进行直接JOIN的交互操作，因为这将导致行的复制，从而导致错误的值。取而代之的是，我们在做SUM之前，先在客户基础上JOIN在客户端基础上每个表中的所有值。另外，由于某些客户端在每个表中都没有条目，因此您必须在结果上使用LEFT JOIN和COALESCE，以便空行不会导致SUM变为NULL。此查询应为您提供所需的结果：

SELECT c.id, c.name,
       COALESCE(t.transactions, 0) + COALESCE(o.amounts, 0) - COALESCE(p.payments, 0) AS amount
FROM client c
LEFT JOIN (SELECT id, SUM(load_amount) + SUM(additional) AS transactions
           FROM transaction
           GROUP BY id) t on t.id = c.id
LEFT JOIN (SELECT id, SUM(amount) AS amounts
           FROM other_loan
           GROUP BY id) o ON o.id = c.id
LEFT JOIN (SELECT id, SUM(payment_amount) AS payments
           FROM payment
           GROUP BY id) p ON p.id = c.id
GROUP BY c.id

输出（用于您的示例数据）：

id  name        amount
1   Robin       8718
2   Cinderella  21
3   Leomar      0

Demo on SQLFiddle

多个mysql表列的总和，减和联接

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