Question

我有以下查询：

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

显示销售订单列表，小计和连接的订单。当有多个po连接到同一个销售订单时，它会返回每个po行的小计。我希望它只显示该销售订单第一行的小计。

example data

Answer 1

如果您使用的是SQL Server 2012，则可以使用LAG将值与上一行进行比较。我使用它来比较前一行的值 - 我比较SalesOrderID和PreviousSalesOrderID - 如果它们不同，您就知道要填写SubTotal列。

解决方案：

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

输出（与预期输出相同）：

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

如果行sql 2，则具有相同ID的多行仅从一列返回数据

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