mysql - 构建 SQL 查询来连接三个表以获取消息传递信息

Question

我有以下三个消息系统表:

`messaging_messagethread`
- id
- subject
- initiator_id # who creates the thread
- recipient_id

`messaging_message`
- id
- thread_id
- content
- timestamp
- sender_id

`messaging_messagestatus` # a status will be created for each recipient of a message
- id
- message_id
- recipient_id
- status

给定一个用户，我需要构建一个查询来获取以下信息:

• 显示线程 ID(不同)，
该线程中最新消息的
• 内容和时间戳
• 删除包含最新消息status='deleted'的所有话题。

这是我到目前为止所拥有的:

SELECT DISTINCT thread.id as thread_id, timestamp.timestamp 
    FROM messaging_messagethread thread 
INNER JOIN 
    (SELECT thread_id, MAX(timestamp) as timestamp
      FROM messaging_message GROUP BY thread_id) timestamp
      ON thread.id = timestamp.thread_id
WHERE initiator_id = 4 OR thread.recipient_id = 4 ORDER BY timestamp.timestamp DESC

这给了我按最近时间戳排序的不同线程 ID。 (我的三点中的第一点)。我将如何构建整个查询？

Answer 1

您可以使用相关子查询来获取特定线程的最新消息。试试这个:

SELECT 
    a.id, 
    b.content, 
    b.timestamp
FROM
    messaging_messagethread a
INNER JOIN
    messaging_message b ON a.id = b.thread_id 
WHERE 
    b.timestamp = 
    (
        SELECT MAX(timestamp) 
        FROM messaging_message 
        WHERE thread_id = a.id
    )
    AND b.id NOT IN
    (
        SELECT message_id
        FROM messaging_messagestatus
        WHERE status = 'deleted'
    )
    AND 4 IN (a.initiator_id, a.recipient_id)
ORDER BY
    b.timestamp DESC

如果我理解正确的话，我相信这就是你想要的。