Sql server 在SQL Server联接中显示空值

我正在使用SQL Server。我有三张桌子：

特布卢瑟

特布拉迪特

特伯伦

tblAudit有4列：

nUserId，nID：这两列指向tblUser

vFromValue，vToValue：这两列指向tblEnum

现在，我需要根据tbludit表中的id显示tblUser和tblEnum的实际值。 我编写的查询如下所示：

SELECT A.aEventID,
U.tName AS MakerChecker,
U2.tName AS OnUser,
VLE.tDisplayName AS FromValue,
VLE2.tDisplayName AS ToValue,
A.dChangeTime AS Timestamp
FROM tblAudit A INNER JOIN tblUser U ON A.nUserId = U.aUserId
INNER JOIN tblUser U2 ON A.nID = U2.aUserId
INNER JOIN tblEnum VLE ON A.vFromValue = VLE.nIndex OR (A.vFromValue IS NULL)
INNER JOIN tblEnum VLE2 ON  A.vToValue = VLE2.nIndex OR (A.vToValue IS NULL)

由于某些行的vFromValue和vToValue列的审核表中的值为null，因此这些值不是null，而是前一个值。

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如何通过更改上述查询完整地显示空值？请帮助。

如果我理解您的问题，请尝试对最后两行使用左连接（并删除或之后的条件）。

由于

tblAudit.vFromValue

和

tblAudit.vToValue

具有

NULL

s，请尝试以下操作：

SELECT A.aEventID,
       U.tName AS MakerChecker,
       U2.tName AS OnUser,
       VLE.tDisplayName AS FromValue,
       VLE2.tDisplayName AS ToValue,
       A.dChangeTime AS Timestamp
FROM 
     ( SELECT aEventID, nUserId, nID, dChangeTime  
            , COALESCE(vFromValue, -9999) AS vFromValue   --- some non-existent
            , COALESCE(vToValue, -999) AS vToValue        --- value
       FROM tblAudit
     ) AS A 
  INNER JOIN tblUser U
    ON A.nUserId = U.aUserId
  INNER JOIN tblUser U2 
    ON A.nID = U2.aUserId
  LEFT JOIN tblEnum VLE 
    ON A.vFromValue = VLE.nIndex
  LEFT JOIN tblEnum VLE2 
    ON  A.vToValue = VLE2.nIndex

或者这个：

SELECT A.aEventID,
       U.tName AS MakerChecker,
       U2.tName AS OnUser,
       ( SELECT VLE.tDisplayName
         FROM tblEnum VLE 
         WHERE A.vFromValue = VLE.nIndex
       ) AS FromValue,
       ( SELECT VLE2.tDisplayName
         FROM tblEnum VLE2 
         WHERE A.vToValue = VLE.nIndex
       ) AS ToValue,
       A.dChangeTime AS Timestamp
FROM tblAudit AS A 
  INNER JOIN tblUser U
    ON A.nUserId = U.aUserId
  INNER JOIN tblUser U2 
    ON A.nID = U2.aUserId

已经做了：）没有帮助。然而，我尝试了其他解决问题的办法，但我认为这不是一个干净的解决办法，而是达到了目的。将其作为答案发布。如果有人找到更好的解决方案，请发布。谢谢