here's table t:
winner_id | loser_id
----------+---------
1 | 2
1 | 2
1 | 3
2 | 1
2 | 3
select winner_id as id, count(*) as wins from t group by winner_id
gives me table x:
id | wins
---+-----
1 | 3
2 | 2
select loser_id as id, count(*) as loses from t group by loser_id
gives me table y:
id | loses
---+------
1 | 1
2 | 2
3 | 2
select id, wins, loses from x full outer join y on x.id=y.id
gives me table z:
id | wins | loses
---+------+------
1 | 3 | 1
2 | 2 | 2
3 | null | 2
except mysql 5 doesn't support outer join! the above query with inner join would get me
id | wins | loses
---+------+------
1 | 3 | 1
2 | 2 | 2
and NOT include player with id=3 because he hasn't both won AND lost some games (he's only lost so far).