如何在子查询中使用主查询中的列？

Question

我有一个表总计列发票。然后我有一张表格（通常有多张付款到一张发票​​）。我需要列出余额，即Invoice.Total的差额 - （在该发票上进行的付款总额）。这就是我（呵呵雅Azure的使用SQL Server）的

select I.Invoice_Id, 
     I.Total - (select sum(Amount) from Payments P 
        where I.Invoice_Id = P.Invoice_Id) as Balance, 
     Q.Quote_Id, 
     Q.Description, 
     Q.Vendor_Num 
from Invoice as I 
    inner join Payments as P on I.Invoice_Id = P.Invoice_Id 
    inner join Quote as Q on Q.Quote_Id = I.Quote_Id; 

最终，这将是展示的发票已经欠平衡什么看法。如果我删除子查询中的位置，它会给我一个答案，但它是所有付款的总和。我只想要该发票上的付款总额。任何帮助，将不胜感激。

感谢

Answer 1

有两种方法可供。你可以通过子查询或分组。如果你正在做一个子查询，你不需要主查询中的表。此外，支付的内部联接意味着没有支付的发票将不会被查询返回。在未满足I.Invoice_Id = P.Invoice_Id时，将其更改为Group By示例中的左外连接将返回NULL行。

组方：

SELECT I.Invoice_Id, 
     I.Total - sum(ISNULL(P.Amount,0)) AS Balance, 
     Q.Quote_Id, 
     Q.Description, 
     Q.Vendor_Num 
    FROM Invoice AS I 
    JOIN Quote AS Q on Q.Quote_Id = I.Quote_Id 
    LEFT JOIN Payments AS P on I.Invoice_Id = P.Invoice_Id 
GROUP BY I.Invoice_Id, I.Total, Q.Quote_Id, Q.Description, Q.Vendor_Num 

子查询：

SELECT I.Invoice_Id, 
     I.Total - (SELECT ISNULL(SUM(Amount),0) FROM Payments P WHERE P.Invoice_Id = I.Invoice_Id) AS Balance, 
     Q.Quote_Id, 
     Q.Description, 
     Q.Vendor_Num 
    FROM Invoice AS I 
    JOIN Quote AS Q on Q.Quote_Id = I.Quote_Id 

Answer 2

我怀疑你的查询（每支付一式两份）返回多个结果，因为你是joining在payments表。

一种选择是将join删除到payments表。下面是其移动correlated subquery到join另一种选择：

select I.Invoice_Id, 
     I.Total - p.SumAmount as Balance, 
     Q.Quote_Id, 
     Q.Description, 
     Q.Vendor_Num 
from Invoice as I 
    inner join Quote as Q on Q.Quote_Id = I.Quote_Id; 
    inner join (
     select invoice_id, sum(amount) SumAmount 
     from Payments 
     group by invoice_id) as P on I.Invoice_Id = P.Invoice_Id