假定参照完整性和Postgres 9.4：

Assuming referential integrity and Postgres 9.4:

SELECT *, total - wins - ties AS losses
FROM (
   SELECT count(*) AS total
        , count(*) FILTER (WHERE m.winner = um.team) AS wins
        , count(*) FILTER (WHERE m.winner = 3) AS ties
   FROM   users_matches um
   JOIN   matches m ON m.id = um.match_id
   WHERE  um.user_id = 123;  -- for one given user
) sub;

关于总计 FILTER 子句（引入Postgres 9.4）：

About the aggregate FILTER clause (introduced with Postgres 9.4):

• 如何简化此游戏统计信息查询？

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