您可以使用如下所示的查询，通过会话获取当前用户与最后一条消息的所有会话：

SELECT users.id,
       users.name,
       messages.conversation_id,
       messages.message_id,
       messages.message_text,
       messages.message_date,
       messages.seen
FROM
  (SELECT conversations.conversation_id,
          IF(conversations.from_user = <current_user_id>, conversations.to_user, conversations.from_user) AS interlocutor_id,
          max(messages.message_id) AS last_message_id
   FROM conversations
   LEFT JOIN messages ON conversations.conversation_id = messages.conversation_id
   WHERE convesations.from_id = <current_user_id>
     OR conversations.to_id = <current_user_id>
   GROUP BY conversations.conversation_id) AS t
LEFT JOIN users ON users.id = t.intercolutor_id
LEFT JOIN messages ON messages.message_id = t.last_message_id

如果需要使用以下方法获取当前用户与最后一条indox消息的所有对话：

SELECT users.id,
       users.name,
       messages.conversation_id,
       messages.message_id,
       messages.message_text,
       messages.message_date,
       messages.seen
FROM
  (SELECT conversations.conversation_id,
          IF(conversations.from_user = <current_user_id>, conversations.to_user, conversations.from_user) AS interlocutor_id,
          max(messages.message_id) AS last_message_id
   FROM conversations
   LEFT JOIN messages ON conversations.conversation_id = messages.conversation_id
   WHERE (convesations.from_id = <current_user_id>
          OR conversations.to_id = <current_user_id>)
     AND messages.user_id <> <current_user_id>
   GROUP BY conversations.conversation_id) AS t
LEFT JOIN users ON users.id = t.intercolutor_id
LEFT JOIN messages ON messages.message_id = t.last_message_id

但我认为最好的方法是重写数据库方案，并在“conversations”表中添加最后一条消息的id。它将使查询更加优化
更新时间：
如果需要获取与当前用户进行对话的所有用户的列表：

SELECT t.conversation_id,
       users.id,
       users.name
FROM
  (SELECT conversation_id,
          IF(from_user = <current_user_id>, to_user, from_user) AS interlocutor_id          
   FROM conversations   
   WHERE from_id = <current_user_id>
     OR to_id = <current_user_id>) AS t
LEFT JOIN users ON users.id = t.intercolutor_id

p、 你必须替换 <current_user_id> 到当前用户的实际标识符

SELECT conversation FROM
        conversations

WHERE (conversations.from_user = <user parameter>
OR conversations.to_user = <user parameter>) 
AND conversations.from_user <> conversations.to_user