Question

I have the sql schema like this:

ID    | Like
______|_______ 
p1    |   2
p1    |   3
p1    |   4
p2    |   3
p2    |   2
p3    |   2
p3    |   3
p3    |   4
p4    |   3
p4    |   2

So I have to Select pairs of people, who like same things. (In this example: [p1,p3] and [p2,p4]). All ‘like’ should be same, so [p1,p2] is wrong!
How can I do that?

Ahead thank you for the answers!

Answer 1

This is a relational division operation. You can do this with a combination of NOT EXISTS clauses, e.g.:

SELECT a.ID AS ID1
      ,b.ID AS ID2
FROM   (SELECT DISTINCT ID FROM mytable) a
      ,(SELECT DISTINCT ID FROM mytable) b
WHERE  a.ID < b.ID
AND    NOT EXISTS
       ( SELECT a2.Like
         FROM   mytable a2
         WHERE  a.ID = a2.ID
         MINUS
         SELECT b2.Like
         FROM   mytable b2
         WHERE  b.ID = b2.ID
       )
AND    NOT EXISTS
       ( SELECT b2.Like
         FROM   mytable b2
         WHERE  b.ID = b2.ID
         MINUS
         SELECT a2.Like
         FROM   mytable a2
         WHERE  a.ID = a2.ID
       );

ID1 ID2
=== ===
p1  p3
p2  p4