Question

我正在尝试获取消息列表，一个表是所有未读消息的列表，另一个是所有已读消息的列表。我希望未读邮件在最后一次更新时排序，以便最新邮件始终位于顶部。

我写了以下查询，除了我得到一个错误，即订单依据未与联合啮合。我尝试将两个语句都用括号括起来，但是顺序错误。

SELECT threads.id AS thread, 
       updated_at 
FROM   threads 
WHERE  threads.id IN (SELECT thread_id 
                      FROM   posts 
                      WHERE  posts.id IN (SELECT post_id 
                                          FROM   post_recipients 
                                          WHERE  status = 1 
                                             AND 
                             user_id = 'b1367cad-e1ea-31ba-beb9-2b53559eea17')) 
ORDER  BY updated_at DESC 
UNION 
SELECT thread_id AS thread, 
       updated_at 
FROM   thread_assignments 
WHERE  user_id = 'b1367cad-e1ea-31ba-beb9-2b53559eea17' 
   AND status = 0 
   AND thread_id NOT IN (SELECT threads.id AS thread 
                         FROM   threads 
                         WHERE  threads.id IN (SELECT thread_id 
                                               FROM   posts 
                                               WHERE 
                                posts.id IN (SELECT post_id 
                                             FROM   post_recipients 
                                             WHERE  status = 1 
                                                AND 
       user_id = 'b1367cad-e1ea-31ba-beb9-2b53559eea17')) 
                        ) 
ORDER  BY updated_at DESC;

要清楚，我不希望由update_at排序的最终表，因为这可能会使已读消息比未读消息高。我要单独订购2张桌子，然后粘在一起。

Answer 1

按照Teson的建议，创建一个附加字段，以便您可以将这两种类型分开

SELECT threads.id AS thread, 
       updated_at ,
       0 as union_source
FROM   threads 
WHERE  threads.id IN (SELECT thread_id 
                      FROM   posts 
                      WHERE  posts.id IN (SELECT post_id 
                                          FROM   post_recipients 
                                          WHERE  status = 1 
                                             AND 
                             user_id = 'b1367cad-e1ea-31ba-beb9-2b53559eea17')) 
UNION 
SELECT thread_id AS thread, 
       updated_at, 
       1 as union_source
FROM   thread_assignments 
WHERE  user_id = 'b1367cad-e1ea-31ba-beb9-2b53559eea17' 
   AND status = 0 
   AND thread_id NOT IN (SELECT threads.id AS thread 
                         FROM   threads 
                         WHERE  threads.id IN (SELECT thread_id 
                                               FROM   posts 
                                               WHERE 
                                posts.id IN (SELECT post_id 
                                             FROM   post_recipients 
                                             WHERE  status = 1 
                                                AND 
       user_id = 'b1367cad-e1ea-31ba-beb9-2b53559eea17')) 
                        ) 
ORDER  BY 
      union_source,
      updated_at DESC;

如何在工会中订购2张桌子？

1 个答案: