Mysql 使用sql sum函数得到错误的结果

我有三张桌子：

select 
    c.c_name, 
    sum(s.net_amount) - sum(cp.recived_amount) as amount 
from customer_payments cp
inner join customer c 
    on c.c_id = cp.customer_id 
inner join sale s 
    on s.cId = c.cId 
group by 
    c.c_name 
having 
    sum(cp.net_amount) - sum(recived_amount) !=0

我想把净金额和收到的金额相加，再减去两者。

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通过内部联接，当我将两行相加时，它不会给出正确的结果。

一个问题是，您为每个客户都得到一个笛卡尔积。另一个原因是，当没有匹配项时，可能会丢失行

您可以通过使用左连接和预聚合值来解决这些问题：

Customer(cId)(cName)
Sale(cId)(net_amount)
Customer_payment(cId)(received_amount)

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实际上不需要外部聚合，除非给定客户具有多个相同名称的id。

您使用的是SQL Server还是MySQL？请显示示例数据、预期结果和实际结果。如果有多个客户付款与销售相关，则销售数字将在您的结果中多次出现，而sales.net_金额的总和将比您可能预期的要大。

select c.c_name, sum(s.net_amount) - sum(cp.received_amount) as amount
from customer c left join
     (select cp.customer_id, sum(cp.received_amount) as receivedamount
      from customer_payments cp
      group by cp.customer_id
     ) cp 
     on c.c_id = cp.customer_id left join
     (select s.cId, sum(s.net_amount) as net_amount
      from sale s
      group by s.cId
     ) s
     on s.cId = c.cId
group by c.c_name
having sum(cp.net_amount)-sum(received_amount) <> 0;