在SQL中连接表时出现问题

Question

SELECT MID, FAD.FirstOpenedDate ,LCD.LastCloseDate
FROM mwMaster.dbo.Merchant M
JOIN        (
            SELECT MerchID, MIN(moddate) AS FirstOpenedDate
            FROM mwMaster.dbo.MerchantStatusHistory
            GROUP BY MerchID
            )   FAD ON FAD.MerchID = M.MerchID 
LEFT JOIN   (
            SELECT MerchID, MAX(moddate) AS LastCloseDate
            FROM mwMaster.dbo.MerchantStatusHistory
            GROUP BY MerchID
            )   LCD ON LCD.MerchID = M.MerchID
JOIN        (
            SELECT merchid ,avg(Transactions) ,avg(Profit) 
            FROM mwMaster.dbo.ResidualSummary RS
            WHERE RS.Date_Processed < LCD.LastCloseDate
            GROUP BY Merchid    
            )   R ON R.MerchID = M.MerchID 

我在执行以下加入时遇到问题.我之前遇到过这个问题并使用临时表但想知道我做错了什么.基本上不起作用的线是倒数第三."<LCD.LastClostDate"表示无法绑定.是否可以使用我在上面的嵌套查询中创建的LCD值(在该查询中我以类似的方式使用M表,但我没遇到任何问题)？我在想,因为LCD表是动态创建的,它不能在嵌套查询中使用,但这只是我的猜测.

有任何想法吗？

另外,我还看到人们使用CROSS和OVER.不熟悉它是如何工作的,但可能适用于此处？

Answer 1

我认为虽然没有经过测试,但您可以在SQL 2005+中将您的JOIN更改为CROSS APPLY

SELECT MID, FAD.FirstOpenedDate ,LCD.LastCloseDate
FROM mwMaster.dbo.Merchant M
JOIN        (
            SELECT MerchID, MIN(moddate) AS FirstOpenedDate
            FROM mwMaster.dbo.MerchantStatusHistory
            GROUP BY MerchID
            )   FAD ON FAD.MerchID = M.MerchID 
LEFT JOIN   (
            SELECT MerchID, MAX(moddate) AS LastCloseDate
            FROM mwMaster.dbo.MerchantStatusHistory
            GROUP BY MerchID
            )   LCD ON LCD.MerchID = M.MerchID
CROSS APPLY(
        SELECT merchid ,avg(Transactions) ,avg(Profit) 
        FROM mwMaster.dbo.ResidualSummary RS
        WHERE RS.Date_Processed < LCD.LastCloseDate
        GROUP BY Merchid    
        )   R ON R.MerchID = M.MerchID 

但是使用CTE可能更容易

 WITH LCD AS (SELECT MerchID, MAX(moddate) AS LastCloseDate
        FROM mwMaster.dbo.MerchantStatusHistory
        GROUP BY MerchID),
  R AS (
              SELECT merchid ,avg(Transactions) ,avg(Profit) 
              FROM mwMaster.dbo.ResidualSummary RS
                   INNER JOIN LCD on 
                   LCD.MERCHID = RS.MERCHID
              WHERE RS.Date_Processed < LCD.LastCloseDate
              GROUP BY Merchid    
            )

SELECT MID, FAD.FirstOpenedDate ,LCD.LastCloseDate
FROM mwMaster.dbo.Merchant M
JOIN        (
            SELECT MerchID, MIN(moddate) AS FirstOpenedDate
            FROM mwMaster.dbo.MerchantStatusHistory
            GROUP BY MerchID
            )   FAD ON FAD.MerchID = M.MerchID 
LEFT JOIN LCD ON LCD.MerchID = M.MerchID
LEFT JOIN R ON R.MerchID = M.MerchID