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

Here's one way using UNPIVOT:

;WITH
    cte AS
    (
        SELECT      CASE WHEN t1.p_x <> t2.p_x THEN 1 ELSE 0 END As p_x,
                    CASE WHEN t1.p_y <> t2.p_y THEN 1 ELSE 0 END As p_y,
                    CASE WHEN t1.p_z <> t2.p_z THEN 1 ELSE 0 END As p_z
        FROM        MyTable t1, MyTable t2
        WHERE       t1.ID = 11 AND t2.ID = 12 -- enter the two revisions to compare here
    )

SELECT      *
FROM        cte
UNPIVOT     (
                Changed FOR ColumnName IN (p_x, p_y, p_z)
            ) upvt
WHERE       upvt.Changed = 1

You have to add code to handle NULLs during the comparisons. You can also build the query dynamically if there are lots of columns in your table.