Question

你好基本上我试图将facebook上的邮件系统复制到我的网站上。

这是逻辑...... “当user1创建一个新消息发送给user7时，创建一个新线程，其thread_id为1（表：messages_thread），并在表中插入一个新条目：消息为message_id 1（表：消息）。当user7 REPLYS时到user1的消息，创建了message2，它的thread_id为1。

现在，当用户1创建发送给用户7的新消息时，创建了线程2，并创建了消息3。当user7回复thread2时，会创建消息4（希望你得到逻辑。）

一切都很好。唯一的问题是我需要在线程中选择最新的消息但是我遇到了sql的问题，

我现在的这个sql ......

SELECT max(message_id) message_id, m.thread_id, m.body, m.user_id,m.to_id, m.message_status, m.new, m.date, u.id, u.displayname, u.username, u.profile_img
FROM messages m INNER JOIN users u ON u.id = m.user_id
WHERE to_id = 7  AND (message_status = 'unread' or message_status='read' or message_status='saved') 
group by thread_id Order by message_id Desc LIMIT 10

制作此...

+------------+-----------+----------------------+---------+-------+----------------+-----+------------+----+--------------+----------+-------------+
| message_id | thread_id | body                 | user_id | to_id | message_status | new | date       | id | displayname  | username | profile_img |
+------------+-----------+----------------------+---------+-------+----------------+-----+------------+----+--------------+----------+-------------+
|          6 |         2 | Really nice          |       1 |     7 | read           |   0 | 1298617367 |  1 | Kenny  Blake | imkenee  | 28_1        |
|          4 |         1 | Whats good with you? |       1 |     7 | read           |   0 | 1298607438 |  1 | Kenny  Blake | imkenee  | 28_1        |
+------------+-----------+----------------------+---------+-------+----------------+-----+------------+----+--------------+----------+-------------+

这很好，但是一个小问题，它选择每组中的第一行，并尝试选择每组中的最新（最后一行）

我该怎么做？这是表格。谢谢！

表：Messages_thread

+----+---------+----------------+-------------+-----------+---------------+-------------+------------+
| id | user_id | subject        | from_status | to_status | from_s_delete | to_s_delete | date       |
+----+---------+----------------+-------------+-----------+---------------+-------------+------------+
|  1 |       1 | Hey Kenny      | unread      | unread    |             0 |           0 | 1298607438 |
|  2 |       7 | Check out this | unread      | unread    |             0 |           0 | 1298617344 |
+----+---------+----------------+-------------+-----------+---------------+-------------+------------+

表格消息

+------------+-----------+---------+-------+-----------------------------------------------------------+----------------+-----------------+-----+------------+
| message_id | thread_id | user_id | to_id | body                                                      | message_status | is_sent_deleted | new | date       |
+------------+-----------+---------+-------+-----------------------------------------------------------+----------------+-----------------+-----+------------+
|          1 |         1 |       1 |     7 | Whats good with you?                                      | read           |               0 |   0 | 1298607438 |
|          2 |         1 |       7 |     1 | Nothing Kenny just chilling. Whats up with you though???? | read           |               0 |   0 | 1298607473 |
|          4 |         1 |       1 |     7 | Just posted victor how are you man?                       | read           |               0 |   0 | 1298607956 |
|          5 |         2 |       7 |     1 | Look at this poem....                                     | read           |               0 |   0 | 1298617344 |
|          6 |         2 |       1 |     7 | Really nice                                               | read           |               0 |   0 | 1298617367 |
|          7 |         2 |       7 |     1 | Yea i know right :)                                       | unread         |               0 |   0 | 1298617383 |
+------------+-----------+---------+-------+-----------------------------------------------------------+----------------+-----------------+-----+------------+

Answer 1

将子线程中的线程分组，该子查询将返回每个线程的最后一条消息：

SELECT m.message_id, m.thread_id, m.body, m.user_id,
    m.to_id, m.message_status, m.new, m.date, u.id, u.displayname, u.username, u.profile_img
FROM messages m 
  INNER JOIN users u ON u.id = m.user_id
  INNER JOIN (
    SELECT MAX(message_id) MaxMsgIDForThread
    FROM messages
    WHERE to_id = 7
      AND (message_status = 'unread'
        or message_status='read'
        or message_status='saved') 
    GROUP BY thread_id
  ) g ON m.message_id = g.MaxMsgIDForThread
Order by m.message_id Desc
LIMIT 10

可能需要将WHERE移动到外部查询，现在它将选择符合条件的最后一条消息，如果要完全跳过线程，则将其移动到外部查询不满足。

您还应该考虑将消息状态存储为ENUM，以便进行比较。

Answer 2

无法通过
添加订单到组但也许这有效：

SELECT max(message_id) message_id, MAX(m.thread_id), m.body, m.user_id,m.to_id, m.message_status, m.new, m.date, u.id, u.displayname, u.username, u.profile_img
FROM messages m INNER JOIN users u ON u.id = m.user_id
WHERE to_id = 7  AND (message_status = 'unread' or message_status='read' or message_status='saved') 
group by thread_id Order by message_id Desc LIMIT 10

获取每组中的最后一行？

2 个答案: