gistfile1.sql

SELECT DISTINCT people.*, count(my_friends.guid_two) AS coincidence
    FROM entities people
    LEFT JOIN metadata 
         ON (metadata.entity_guid = people.guid)
    LEFT JOIN relationships related_friends 
         ON (related_friends.guid_two = people.guid)
    LEFT JOIN relationships my_friends
         ON (related_friends.guid_one = my_friends.guid_two)
    WHERE my_friends.guid_one = 'ME!' -- indirectly related to me
      AND my_friends.relation = 'friend' 
      AND related_friends.guid_one != 'ME!' -- not related directly to me
      AND related_friends.relation = 'friend'
      AND (metadata.name = 'hobby' AND metadata.value IN ('sport', 'ksiazki')) -- IN my_hobbies
    GROUP BY my_friends.guid_two
    HAVING coincidence >= 1
    ORDER BY coincidence DESC