Question

I’m using SQL Server. I’ve 3 tables :

1. tblUser
2. tblAudit
3. tblEnum

The tblAudit has got 4 columns :

nUserId, nID: These two columns point to the tblUser

vFromValue, vToValue: These two columns point to the tblEnum

Now, I need to show the actual values from the tblUser and tblEnum based on the IDs present in the tblAudit table.
The query that I have written looks something like this :

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)

Because the values in the Audit table is null for the columns vFromValue and vToValue for some rows, those values are not coming as NULL but the previous value.
How can I display the null values intact by changing the above query? Please help.

Answer 1

Since the tblAudit.vFromValue and tblAudit.vToValue have NULLs, try this:

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

or this:

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