Question

Here’s rough example of what I need to accomplish for better understanding:

SampleTable

PrimaryKey SpecialCol1 RandomCol SpecialCol2
    1         aaa       sample1     111
    2         aaa       sample2     222
    3         bbb       sample3     444
    4         aaa       sample4     111
    5         ccc       sample5     444
    6         bbb       sample6     444

Final result should look like this:

PrimaryKey SpecialCol1 RandomCol SpecialCol2
--------------------------------------------
2         aaa       sample2     222
5         ccc       sample5     444

So I just need to select those rows for which combination of SpecialCol1 and SpecialCol2 is unique in that table. I’ve spent a lot of time trying to figure out how it can be done but so far no luck.

Answer 1

Do it in stages.

1. Find the rows where the combination of columns is unique:

   SELECT SpecialCol1, SpecialCol2
     FROM SampleTable -- Thank you for invcluding the tablename
    GROUP BY SpecialCol1, SpecialCol2
   HAVING COUNT(*) = 1;
   

2. Find the other details for the matching rows:

   SELECT s.*
     FROM SampleTable AS s
     JOIN (SELECT SpecialCol1, SpecialCol2
             FROM SampleTable -- Thank you for invcluding the tablename
            GROUP BY SpecialCol1, SpecialCol2
           HAVING COUNT(*) = 1
          ) AS t
       ON t.SpecialCol1 = s.SpecialCol1 AND t.SpecialCol2 = s.SpecialCol2;