如何在子查詢中使用主查詢中的列？

Question

我有一個表總計列發票。然後我有一張表格（通常有多張付款到一張發票​​）。我需要列出餘額，即Invoice.Total的差額 - （在該發票上進行的付款總額）。這就是我（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; 

最終，這將是展示的發票已經欠平衡什麼看法。如果我刪除子查詢中的位置，它會給我一個答案，但它是所有付款的總和。我只想要該發票上的付款總額。任何幫助，將不勝感激。

感謝

Answer 1

有兩種方法可供。你可以通過子查詢或分組。如果你正在做一個子查詢，你不需要主查詢中的表。此外，支付的內部聯接意味着沒有支付的發票將不會被查詢返回。在未滿足I.Invoice_Id = P.Invoice_Id時，將其更改爲Group By示例中的左外連接將返回NULL行。

組方：

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 

子查詢：

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

我懷疑你的查詢（每支付一式兩份）返回多個結果，因爲你是joining在payments表。

一種選擇是將join刪除到payments表。下面是其移動correlated subquery到join另一種選擇：

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