MySQL查詢以顯示發送方和接收方的名稱

Question

我有一個稱為users的表，看起來像這樣：

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

我有一個名為msg的表，看起來像這樣：

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

所以現在我有一個問題，因為我不知道如何將msg.sender（id）加入users.name（name）。

所以基本上我想要結束的事情看起來像這樣：

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

希望這些插圖對我要解釋的內容有所幫助。

Answer 1

只需將users表與msg表join兩次-在發送者上然后在接收者上。

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

您應該使用別名兩次連接用戶表

  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