Question

我有一条＆＃39;消息＆＃39;表格包括列：

message_id, sender_id, receiver_id

一个＆＃39;成员＆＃39;表格包括列：

id, username

我的发件箱查询如下

SELECT message_id, username AS 'receiver_username', sender_id,
receiver_id, time_sent, time_read, replied_to_id,item_id_reference,
subject FROM messages, members WHERE messages.sender_id = members.id 
AND members.username = ?

我希望我的查询根据发件人message_id

返回username

WHERE messages.sender_id = members.id AND members.username = ?

以及基于返回的receiver_id

的收件人用户名

如何在单个查询中执行此操作？

Answer 1

您需要加入成员表两次，一次是发件人名称，一次是receiver_name。一个简单的例子：

SELECT
    s.user_name sender,
    r.user_name receiver
FROM
    messages m
JOIN
    members s ON
    m.sender_id = s.member_id
JOIN
    members r ON
    m.receiver_id = r.member_id

Answer 2

这可以是两次加入members表的替代方法：

SELECT 
  message_id, username, sender_id,
  receiver_id, time_sent, time_read, replied_to_id,item_id_reference,
  subject 
FROM 
  messages msg INNER JOIN  
  members m ON m.id IN (msg.receiver_id, msg.sender_id) 
AND m.username = ?

MySQL SELECT具有多个条件的相同列

2 个答案: