Question

I have a table like so;

id1     id2
1       1
2       1
1       2
3       2
1       3
4       3
1       4
5       4

I’d like to select it in a way that I’d get rows GROUPed by id2, but still preserving both values of id1 for the corresponding rows in the table.

So I’d get a result set like so;

id1     id1     id2
1       2       1
1       3       2
1       4       3
1       5       4

I’ve never been even half good in advanced database queries — how would I go about achieving this?

Answer 1

If you have exactly 2 rows (with 2 values for id1) for every different value of id2, you can use this:

SELECT MIN(id1) AS id1_a
     , MAX(id1) AS id1_b
     , id2
FROM tableX
GROUP BY id2 ;