Question

I am trying to merge 2 databases with the same schema together, and this is one part of it.

I have changed the subject to keep it more understandable – I cannot change this schema, it’s just what I’m working with.

I have a table in both my source and target databases with the following columns:

Car
CarType1
CarType2
CarType3
CarType4

I am trying to write a query that will tell me in the target database, which rows have the same Cars between the 2 databases, but different CarTypes. All I need is a count on the rows that are different.

My query written in english would be:
Bring me back a count of rows where the Car is the same and the CarTypes between the two systems do not match. It doesn’t matter if the CarType is in a different CarType field between the two, just whether all of the values are contained in one of the 4 fields or not.

So if in my source database this row:

Car: Mustang
CarType1: Fast
CarType2: Convertible
CarType3: null
CarType4: null

And in my target database I have this row:

Car: Mustang
CarType1: Fast
CarType2: Convertible
CarType3: Sports
CarType4: null

This would count as a non-match, since it’s a Mustang and because the aggregate of the CarType fields is different. What order the values are in does not matter for this.

How would I write this query? I cannot get a grasp on it.

Answer 1

;WITH SourceT AS (
SELECT 'Toyota' AS Car, 'A' AS CarType1, 'B' AS CarType2, 'C' CarType3, 'D' CarType4 UNION ALL
SELECT 'BMW' AS Car, 'A' AS CarType1, 'B' AS CarType2, 'C' CarType3, 'D' CarType4 UNION ALL
SELECT 'Mustang' AS Car, 'Fast' AS CarType1, 'Convertible' AS CarType2, 'Sports' CarType3, NULL CarType4 
),
TargetT AS (
SELECT 'Toyota' AS Car, 'D' AS CarType1, 'C' AS CarType2, 'B' CarType3, 'A' CarType4 UNION ALL
SELECT 'BMW' AS Car, 'D' AS CarType1, 'C' AS CarType2, 'B' CarType3, 'A' CarType4  UNION ALL
SELECT 'Mustang' AS Car, 'Fast' AS CarType1, 'Convertible' AS CarType2, NULL CarType3, NULL CarType4 )

SELECT *
FROM SourceT s
WHERE NOT EXISTS
(
SELECT * 
FROM TargetT t 
WHERE s.Car = t.Car AND 0 =
(SELECT COUNT(*) FROM 
    ( (
       (SELECT s.CarType1 AS t UNION ALL 
        SELECT s.CarType2 AS t UNION ALL 
        SELECT s.CarType3 AS t UNION ALL 
        SELECT s.CarType4 AS t )
    EXCEPT                
       (SELECT t.CarType1 AS t UNION ALL 
        SELECT t.CarType2 AS t UNION ALL 
        SELECT t.CarType3 AS t UNION ALL 
        SELECT t.CarType4 AS t )
        ) 
    UNION ALL
    (
       (SELECT t.CarType1 AS t UNION ALL 
        SELECT t.CarType2 AS t UNION ALL 
        SELECT t.CarType3 AS t UNION ALL 
        SELECT t.CarType4 AS t )
    EXCEPT                
       (SELECT s.CarType1 AS t UNION ALL 
        SELECT s.CarType2 AS t UNION ALL 
        SELECT s.CarType3 AS t UNION ALL 
        SELECT s.CarType4 AS t )
        )     
        ) T
    )
)

Or a slightly shorter version

SELECT *
FROM SourceT s
WHERE NOT EXISTS
(
SELECT * 
FROM TargetT t 
WHERE s.Car = t.Car AND 
(SELECT t FROM (SELECT s.CarType1 AS t UNION ALL 
                SELECT s.CarType2 AS t UNION ALL 
                SELECT s.CarType3 AS t UNION ALL 
                SELECT s.CarType4 AS t ) D ORDER BY t FOR XML PATH(''))=
(SELECT t FROM (SELECT t.CarType1 AS t UNION ALL 
                SELECT t.CarType2 AS t UNION ALL 
                SELECT t.CarType3 AS t UNION ALL 
                SELECT t.CarType4 AS t ) D ORDER BY t FOR XML PATH(''))
    )