Question

I have a scenario where I need to join two SQL tables and am struggling with how to do it.
Let’s say in table A I have this:

ColA  ColB   ColC   ColD
45     55     17     45
45     55     17     47
45     55     17     49
45     55     17     51

And in Table B I have this:

ColA  ColB   ColC   ColE
45     55     17     55
45     55     17     56
45     55     17     57
45     55     17     58

I need to create a table that looks like this – note only the 4 rows, not the 16 that the inner join I was using produces.

ColA  ColB   ColC   ColD   ColE
45     55     17     45     55
45     55     17     47     56
45     55     17     49     57
45     55     17     51     58

I’m pretty much out of ideas. Both tables will always have the same number of rows. Is there a way to do this using joins, or should I iterate through the table A (ie get the row number) and get the matching row number in Table B?

Any thoughts would be greatly appreciated.

Answer 1

Assuming at least SQL Server 2005

WITH T1
     AS (SELECT *,
                ROW_NUMBER() OVER (PARTITION BY ColA, ColB, ColC ORDER BY ColD)
                RN
         FROM   TableA),
     T2
     AS (SELECT *,
                ROW_NUMBER() OVER (PARTITION BY ColA, ColB, ColC ORDER BY ColE)
                RN
         FROM   TableB)
SELECT T1.ColA,
       T1.ColB,
       T1.ColC,
       T1.ColD,
       T2.ColE
FROM   T1
       JOIN T2
         ON T1.ColA = T2.ColA
            AND T1.ColB = T2.ColB
            AND T1.ColC = T2.ColC
            AND T1.RN = T2.RN