Compare two rows and identify columns whose values are different

Question

The Situation

We have an application where we store machine settings in a SQL table. When the user changes a parameter of the machine, we create a \

Answer 1

You can use unpivot and pivot. The key is to transpose data so that you can use where [11] != [12].

WITH CTE AS (
    SELECT * 
    FROM 
    (
        SELECT ID, colName, val
        FROM tblName
        UNPIVOT
        (
            val
            FOR colName IN ([p_x],[p_y],[p_z])
        ) unpiv
    ) src
    PIVOT
    (
        MAX(val)
        FOR ID IN ([11], [12])
    ) piv
)
SELECT colName
--SELECT *
FROM CTE WHERE [11] != [12]

If there are only a few columns in the table, it's easy to simply put [p_x],[p_y],[p_z], but obviously it's not convenient to type 50 or more columns. Even though you may use this trick to drag and drop, or copy/paste, the column names from the table, it's still bulky. And for that, you may use the SELECT * EXCEPT strategy with dynamic sql.

DECLARE @TSQL NVARCHAR(MAX), @colNames NVARCHAR(MAX)
SELECT @colNames = COALESCE(@colNames + ',' ,'') + [name] 
FROM syscolumns WHERE name  <> 'ID' and id = (SELECT id FROM sysobjects WHERE name = 'tablelName')

SET @TSQL = '
    WITH CTE AS (
        SELECT * 
        FROM 
        (
            SELECT ID, colName, val
            FROM tablelName
            UNPIVOT
            (
                val
                FOR colName IN (' + @colNames + ')
            ) unpiv
        ) src
        PIVOT
        (
            MAX(val)
            FOR ID IN ([11], [12])
        ) piv
    )
    --SELECT colName
    SELECT *
    FROM CTE WHERE [11] != [12]
'
EXEC sp_executesql @TSQL