需要简单加入的帮助

[英]Need help with a simple Join


Oi

Right to the problem.

问题的权利。

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

I have two fields in threads called posterid and lastposterid. Which are the IDs of the thread starter / last poster. What I want to do is to get their names from players table.

我在线程中有两个字段叫做posterid和lastposterid。哪个是线程启动器/最后一张海报的ID。我想做的是从玩家表中获取他们的名字。

But how?

但是怎么样?

3 个解决方案

#1


1  

You can join to the same table twice and give the table a different alias.

您可以两次加入同一个表,并为表提供不同的别名。

This presumes that there always will be a first and last poster, if this is the case then you want an INNER JOIN rather than a LEFT JOIN, you will need to change the select statement to get the relevant fields.

这假设总会有第一张和最后一张海报,如果是这种情况,那么你想要一个INNER JOIN而不是LEFT JOIN,你需要更改select语句来获取相关字段。

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

#2


3  

You just need to join to your players table twice, like this.

你只需要两次加入你的玩家表,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

#3


0  

How about...

怎么样...

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;

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