Add up conditional counts on multiple columns of the same table

Question

I am looking for a \"better\" way to perform a query in which I want to show a single player who he has played previously and the associated win-loss record for each such oppone

Answer 1

Solution with correlated subquery:

SELECT *,
       (SELECT COUNT(*) FROM match WHERE loser_id = p.player_id),
       (SELECT COUNT(*) FROM match WHERE winner_id = p.player_id)
FROM dbo.player p WHERE player_id <> 1

Solution with UNION and conditional aggregation:

SELECT  t.loser_id ,
        SUM(CASE WHEN result = 1 THEN 1 ELSE 0 END) ,
        SUM(CASE WHEN result = -1 THEN 1 ELSE 0 END)
FROM    ( SELECT    * , 1 AS result
          FROM      match
          WHERE     winner_id = 1
          UNION ALL
          SELECT    loser_id , winner_id , -1 AS result
          FROM      match
          WHERE     loser_id = 1
        ) t
GROUP BY t.loser_id