我加入查询返回inncorrect值

Question

我有问题，当我查询sql服务器从不同的三个表检索记录它执行完全不正确的值为SUM([Bills.Extrabill_dollar])和SUM([Receipts.Amount])，波纹管是我的查询请帮助我。

select Customers.SNO, SUM(Bills.Extrabill_dollar) as [ExtraAmount],SUM(Receipts.Amount) as [Received] 
from 
Customers left join Bills on Customers.SNO=Bills.CustomerSNO 
left join Receipts on Customers.SNO=Receipts.CSNO 
group by Customers.SNO 

但如果我用波纹管两个单独的查询返回SUM（Extra_dollar）和SUM（Extra_dollar）
SELECT Bills.CustomerSNO as [CustomerSNO], SUM(Bills.Extrabill_dollar) AS [TotalExtraAmount] from Bills group by Bills.CustomerSNO

SELECT Receipts.CSNO as [CustomerSNO], SUM(Receipts.Amount) AS [TotalReveied] from Receipts group by Receipts.CSNO正确的结果将返回，将不予退还如果通过使用JOIN来组合这些表，请帮助我Dears。

Answer 1

尊敬您的帮助所有的感谢，长途跋涉后，我发现答案：

select c.SNO, c.CName, 
isnull((select SUM(PricePerKwt_dollar) from Bills 
where Bills.CustomerSNO =c.SNO),0.00) as [TotalBills], 
isnull((select SUM(Receipts.Amount) from Receipts 
where Receipts.CSNO = c.SNO),0.00) as [TotalReceipts] 
from Customers c 

Answer 2

通过说你得到不正确的答案，我不知道。

我想因为您使用了LEFT JOIN，所以可能会导致问题。 左连接采用来自Customers的所有值，即使存在不匹配的行，它们将在Bills和Receipts下映射到NULL值。

您可以使用此代码并尝试一下。

SELECT Customers.SNO 
, SUM(Bills.Extrabill_dollar) AS [ExtraAmount] 
, SUM(Receipts.Amount) AS [Received] 
FROM 
Customers INNER JOIN Bills 
ON Customers.SNO=Bills.CustomerSNO 
INNER JOIN Receipts 
ON Customers.SNO=Receipts.CSNO 
GROUP BY Customers.SNO 

Answer 3

select Customers.SNO, SUM(Bills.Extrabill_dollar) as [ExtraAmount],SUM(Receipts.Amount) as [Received] 
from 
Customers right join Bills on Customers.SNO=Bills.CustomerSNO 
right join Receipts on Customers.SNO=Receipts.CSNO 
group by Customers.SNO