如何在SQL中执行以下联接？

Question

假设我有下表GAME

match_id, user_id, score
1, 10, 45
1, 11, 57
2, 10, 39
2, 14, 63

现在，我想执行一个查询，获取玩家10，并像这样显示他的得分以及对手的得分

match_id, user_id, score, opponent_id, opponent_score
1, 10, 45, 11, 57
2, 10, 39, 14, 63

Answer 1

select  P.match_id,
        P.user_id,
        P.score,
        O.user_id as opponent_id,
        O.score as opponent_score
  from  GAME P
  join  GAME O
    on  O.match_id = P.match_id
    and O.user_id <> P.user_id
  where P.user_id = 10
order by P.match_id

使用表别名“ P”代表“玩家”，使用“ O”代表“对手”

Marc指出，这可能因数据库而异。 替代的联接语法（在您偶尔使用的情况下，例如旧的Informix）将是在from上列出两个表，并将join-on子句移到where，例如

  from  GAME P, GAME O
  where O.match_id = P.match_id
    and O.user_id <> P.user_id
    and P.user_id = 10

但join应该最适合。

Answer 2

SELECT
    a.match_id,
    a.user_id AS user_id,
    a.score AS score,
    b.user_id AS opponent_id,
    b.score AS opponent_score
FROM
    game a
JOIN
    game b
ON
    a.match_id = b.match_id
AND
    a.user_id <> b.user_id
WHERE
    a.user_id = 10

编辑：使查询像应该的那样工作。 但是请查看Rup的答案，以更好地完成它。

Answer 3

select
    U.match_id,
    U.user_id,
    U.score,
    O.user_id as opponent_id,
    O.score as opponent_score
from GAME U
    inner join GAME O on 
        U.match_id = O.match_id and
        U.user_id <> O.user_id
where U.user_id = 10