與一列只在一個相同的ID返回數據的多行如果行的sql 2

Question

我有以下查詢：

SELECT dbo.SalesOrder.SalesOrderID, dbo.SalesOrder.SalesOrderNo, dbo.SalesOrder.SubTotal, dbo.PO.PONo 
FROM dbo.SalesOrder 
LEFT OUTER JOIN dbo.PO ON dbo.SalesOrder.SalesOrderID = dbo.PO.SalesOrderID 

這顯示的銷售訂單，其小計和連接寶的名單。當有多個po連接到相同的銷售訂單時，它將返回每個po行的小計。我希望它只在該銷售訂單的第一行顯示小計。

example data

Answer 1

如果你是SQL Server 2012中您可以使用LAG與以前行比較值。我使用它來比較數值與上一行 - 我比較SalesOrderID和PreviousSalesOrderID - 如果它們不同，請填寫SubTotal列。

解決方案：

SELECT SalesOrder.SalesOrderID, SalesOrder.SalesOrderNo, t1.PONo, 
(CASE 
    WHEN (t1.PreviousSalesOrderID IS NULL) OR (t1.PreviousSalesOrderID <> SalesOrder.SalesOrderID) THEN SalesOrder.SubTotal 
END) as SubTotal 
FROM (SELECT SalesOrder.SalesOrderID, PurchaseOrder.PONo, 
    LAG(SalesOrder.SalesOrderID) OVER (ORDER BY SalesOrder.SalesOrderID) AS PreviousSalesOrderID 
    FROM SalesOrder LEFT OUTER JOIN PurchaseOrder ON SalesOrder.SalesOrderID = PurchaseOrder.SalesOrderID) AS t1 
LEFT OUTER JOIN SalesOrder ON SalesOrder.SalesOrderID = t1.SalesOrderID 

輸出（與你的預期輸出）：

SalesOrderID SalesOrderNo PONo SubTotal 
8    S00008   p7  1544 
9    S00009   p8  1644 
9    S00009   p262 NULL 
10    S00010   p263 4922 
10    S00010   p9  NULL 
11    S00011   p10  7805