MySQL的自參照的ID和選擇

Question

我有一個MySQL表這裏Starcraft2brackets：

http://i.stack.imgur.com/welPq.png（重新編輯，所以我可以重新編輯，遺憾第一編輯器）

UID =>參照用戶

id =>索引

opponent =>在此表中引用id，-2被認爲是再見。

我想要做的是提出一個sql語句，它將根據行的uId選擇一個用戶名，以及選擇他們的對手的用戶名。最有建設性的一個我想出迄今是

SELECT u1.username, if(sc2a.opponent = -2, "Bye", u2.username) as username 
FROM Starcraft2brackets AS sc2a 
LEFT JOIN users AS u1 ON u1.id = sc2a.uId 
LEFT JOIN Starcraft2brackets AS sc2b ON sc2a.opponent = sc2b.id 
LEFT JOIN users AS u2 ON sc2b.uId = u2.id 

這確實給我正確的用戶名，但它給了重複的條目，像這樣..

http://i.imgur.com/znbAi.png

SELECT u1.username, IF(sc2a.opponent = -2, "Bye", u2.username) AS username 
FROM Starcraft2brackets AS sc2a 
LEFT JOIN users AS u1 ON u1.id = sc2a.uId 
LEFT JOIN Starcraft2brackets AS sc2b ON sc2a.opponent = sc2b.id 
LEFT JOIN users AS u2 ON sc2b.uId = u2.id 
WHERE u1.username < u2.username 
OR sc2a.opponent = -2 

這給了我準確的結果集。感謝您的幫助stackoverflow.com。

Answer 1

試試這個：

SELECT u1.username, if(u1.oppponent = -2, "Bye", u2.username) as username 
FROM users AS u1 
left join users AS u2 on u1.opponent = u2.id 
join Starcraft2brackets AS sc2a on u1.id = sc2a.uId 
where u1.uid = ?;