[英]How do I perform the following join in SQL?
假設我有下表GAME
match_id, user_id, score
1, 10, 45
1, 11, 57
2, 10, 39
2, 14, 63
現在,我想執行一個查詢,獲取玩家10,並像這樣顯示他的得分以及對手的得分
match_id, user_id, score, opponent_id, opponent_score
1, 10, 45, 11, 57
2, 10, 39, 14, 63
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
使用表別名“ P”代表“玩家”,使用“ O”代表“對手”
Marc指出,這可能因數據庫而異。 替代的聯接語法(在您偶爾使用的情況下,例如舊的Informix)將是在from上列出兩個表,並將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
應該最適合。
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
編輯:使查詢像應該的那樣工作。 但是請查看Rup的答案,以更好地完成它。
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
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