MySQL从一个表中选择所有内容，并从其他两个表中求和

Question

我有3张桌子

发票：id，客户

服务：invioce_id，价格

付款：invoice_id，金额

我想为每个发票选择所有服务价格为amountDue的所有发票，并将付款金额作为amountPaid的所有付款。

因此，例如，如果我有以下行：

发票

id = 1, client = 232
id = 2, client = 535

服务

invoice_id = 1, price = 5.00
invoice_id = 1, price = 10.00
invoice_id = 2, price = 20.00

付款方式

invoice_id = 1, amount = 7.00
invoice_id = 2, amount = 12.00
invoice_id = 2, amount = 8.00

我希望所有发票行的查询结果如下所示：

发票

id = 1, client = 232, amountDue = 15.00, amountPaid = 7.00
id = 2, client = 535, amountDue = 20.00, amountPaid = 20.00

我有这样的查询：

SELECT invoices.*, 
sum(services.price) AS amountDue, 
sum(payments.amount) AS amountPaid 
FROM invoices 
LEFT JOIN services ON services.invoice = invoices.id 
LEFT JOIN payments ON invoices.id = payments.invoice 
GROUP BY invoices.id

但所产生的金额已乘以每张发票的服务数量。

有没有办法通过一个查询提取所有数据？

Answer 1

您有两个子表，在各自的联接中返回的行数不同。 如果您在没有分组/求和的情况下运行查询，则最终结果是：

+------+-----------+-------+-----------+--------+
| id   | serviceid | price | paymentid | amount |
+------+-----------+-------+-----------+--------+
|    1 |         1 |  5.00 |         1 |   7.00 |
|    1 |         1 | 10.00 |         1 |   7.00 |
|    2 |         2 | 20.00 |         2 |  12.00 |
|    2 |         2 | 20.00 |         2 |   8.00 |
+------+-----------+-------+-----------+--------+

请注意，发票＃1的付款金额$ 7和发票＃2的服务价格是如何重复的。 MySQL试图通过复制表中行较少的值来填补查询结构产生的“漏洞”。

为了使这种查询有效，您需要使用相关的子查询，以便每个子查询都可以进行自己的求和，而不受其他表的行数限制的约束：

select invoices.id,
   (select sum(price) from services where services.iid = invoices.id ) AS service_price,
   (select sum(amount) from payments where payments.iid = invoices.id) AS payment_amount
FROM invoices;

产生

+------+---------------+----------------+
| id   | service_price | payment_amount |
+------+---------------+----------------+
|    1 |         15.00 |           7.00 |
|    2 |         20.00 |          20.00 |
+------+---------------+----------------+