mysql - mysql表分组时检索最后一条记录

Question

我有表t_message，它收集用户和用户之间的对话。

这是表结构。

 id_message sender_user_id receiver_user_id message 
1          2              1                test 1
2          1              2                test 2
3          2              1                test 3
4          1              2                test 4

with that table, i have an objective to collect group of conversation for user, and as example i want to colletct groups of conversation beetween user 1 and user 2. using this query

select * from ( select * from t_message where receiver_user_id = 1 order by id_message DESC ) group by sender

结果是

id_message sender_user_id receiver_user_id message 
3          2              1                test 3

它显示用户 1 和用户 2 之间的对话组，但不显示用户 1 和用户 2 之间的对话。它只显示用户 2 或发件人的最后一次对话。

我需要什么查询来收集用户之间的一组对话，并检索该对话的最后记录。 有什么建议吗？

哦，顺便说一句，我很抱歉我的英语不好，我希望你明白。

Answer 1

您可以连接发送者和接收者以形成对话

select a.id, a.conversation, b.sender_user_id, b.receiver_user_id, b.message
from (
  select max(id_message) id,
         if(sender_user_id>receiver_user_id,
            concat(receiver_user_id,',',sender_user_id),
            concat(sender_user_id,',',receiver_user_id)) conversation
  from t_message
  group by conversation) a
join t_message b on a.id = b.id_message;

fiddle