需要简单加入帮助

Question

Oi

正确的问题。

SELECT *,t.id AS threadid FROM threads t 
LEFT JOIN players p on p.id = t.last_poster 
WHERE t.boardid = $boardid 

我在线程调用posterid和lastposterid两个字段。哪些是线索起始者/最后一张海报的ID。我想要做的是从玩家桌上获得他们的名字。

但是如何？

Answer 1

你可以加入到同一个表两次，给表不同的别名。

这假定始终会有第一张和最后一张海报，如果是这种情况，那么您需要INNER JOIN而不是LEFT JOIN，则需要更改select语句以获取相关字段。

SELECT t.id AS threadid, playerFirst.name AS FirstPoster, playerLast.name as LastPoster 
FROM threads t 
INNER JOIN 
    players playerFirst ON playerFirst.id = t.posterid 
INNER JOIN 
    players playerLast ON playerLast.id = t.lastposterid 

Answer 2

你只需要加入到你的球员表两次，就像这样。

SELECT 
    threads.*, 
    starterPlayer.*, 
    lastPosterPlayer.* 
FROM 
    threads 
LEFT OUTER JOIN 
    players starterPlayer 
ON 
    starterPlayer.id = threads.posterid 
LEFT OUTER JOIN 
    players lastPosterPlayer 
ON 
    lastPosterPlayer.id = threads.lastposterid 

Answer 3

......怎么

SELECT *, 
    (SELECT name 
     FROM players 
     WHERE players.id = threads.posterid) AS poster, 
    (SELECT name 
     FROM players 
     WHERE players.id = threads.lastposterid) AS last_poster 
    FROM threads;