MySQL查询以显示发件人和收件人的姓名

Question

我有一个名为users的表，如下所示：

 +----+----------------+
 | id | name           | 
 +----+----------------+
 |  1 | Blake          | 
 |  2 | Jenn           | 
 +----+----------------+

我有一个名为msg的表，如下所示：

 +----+----------------+----------------+
 | id | sender         | receiver       | 
 +----+----------------+----------------+
 |  1 | 1              | 2              |
 |  2 | 2              | 1              |
 +----+----------------+----------------+

所以现在我遇到了一个问题，因为我无法弄清楚如何将msg.sender（id）加入users.name（name）。

基本上我想要最终得到的东西，看起来有点像这样：

 +----+----------------+----------------+----------------+----------------+
 | id | sender         | sender_name    | receiver       | receiver_name  |
 +----+----------------+----------------+----------------+----------------+
 |  1 | 1              | Blake          | 2              | Jenn           |
 |  2 | 2              | Jenn           | 1              | Blake          |
 +----+----------------+----------------+----------------+----------------+

我希望这些插图对我试图解释的内容有所帮助。

Answer 1

join表只需users两次msg表 - 一旦发件人，然后是接收者。

select m.*,
    s.name as sender_name,
    r.name as receiver_name
from msg m
join users s on m.sender = s.id
join users r on m.receiver = r.id;

Answer 2

您应该使用别名

两次加入用户表

  select  msg.sender, u1.name  as sender_name, msg.receiver, u2.name as receiver_name
  from msg
  inner join users u1 on u1.id =  msg.sender
  inner join users u2 on u2.id =  msg.receiver