mysql - 两个内连接查询不运行？

Question

我想在两个表中使用内部。
我的桌子是users和relations（users再次）。我想加入relationsonusers并sender_id再次加入reveiver_id。
我的示例代码是：

select * from 
(relations inner join users on relations.sender_id = users.userid) 
inner join users on relations.reciever_id = users.userid

但是这段代码没有运行。为什么？

Answer 1

如果你想使用子查询，那么你可以使用这个查询 -

SELECT * FROM 
  (SELECT * FROM `relations`
   INNER JOIN `users`
     ON `relations`.`sender_id` = `users`.`userid`) t
INNER JOIN `users`
  ON t.`reciever_id` = `users`.`userid`

但它与 -

SELECT * FROM `relations`
INNER JOIN `users`
  ON `relations`.`sender_id` = `users`.`userid`
INNER JOIN `users`
  ON `relations`.`reciever_id` = `users`.`userid`

Answer 2

SELECT * 
FROM `relations` AS r INNER JOIN 
`users` AS u1 on r.`sender_id` = u1.`userid` INNER JOIN 
`users` AS u2 on r.`reciever_id` = u2.`userid`