Question

我想在两张桌子中使用内心。
我的表格为users，relations和users（再次）。我想relations与users sender_id加入reveiver_id并再次加入select * from (relations inner join users on relations.sender_id = users.userid) inner join users on relations.reciever_id = users.userid。
我的示例代码是：

{{1}}

但此代码未运行。为什么呢？

Answer 1

如果要使用子查询，则可以使用此查询 -

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 -

相同

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`

两个内连接查询没有运行？

2 个答案: