Question

Am试图对具有更多未读消息的用户进行排序，使其首先出现在mysql结果中，同时还包括具有已读消息的用户最后出现

Am使用mysql 5.6.17 表结构

+-----------+--------------+------+-----+---------+----------------+
| Field     | Type         | Null | Key | Default | Extra          |
+-----------+--------------+------+-----+---------+----------------+
| msgID     | int(11)      | NO   | PRI | NULL    | auto_increment |
| userID    | int(11)      | NO   |     | NULL    |                |
| msgText   | varchar(255) | NO   |     | NULL    |                |
| msgStatus | varchar(255) | NO   |     | NULL    |                |
| userName  | varchar(255) | NO   |     | NULL    |                |
+-----------+--------------+------+-----+---------+----------------+

我的数据没有排序

+-------+--------+-------------------+-----------+----------+
| msgID | userID | msgText           | msgStatus | userName |
+-------+--------+-------------------+-----------+----------+
|     1 |      1 | hi                | unread    | Francis  |
|     2 |      2 | hello             | unread    | Emma     |
|     3 |      1 | good              | unread    | Francis  |
|     4 |      1 | your not easy     | read      | Francis  |
|     5 |      2 | just no that      | unread    | Emma     |
|     6 |      2 | don't lose it bro | unread    | Emma     |
|     7 |      2 | good keep it up   | unread    | Emma     |
|     8 |      3 | i don't hate it   | unread    | John     |
+-------+--------+-------------------+-----------+----------+

如果我运行组查询"select userID, userName FROM msg GROUP BY userID"; 它将结果分组

+--------+----------+
| userID | userName |
+--------+----------+
|      1 | Francis  |
|      2 | Emma     |
|      3 | John     |
+--------+----------+

但是我需要那些“ msgStatus”等于“未读”的人出现在顶部，以便甚至包括那些只对“ msgStatus”读过的人，在此先谢谢大家

select userID, userName FROM msg GROUP BY userID;

Answer 1

按sum(msgStatus = 'unread')降序排列：

select userID, userName 
FROM msg 
GROUP BY userID
order by sum(msgStatus = 'unread') desc

Answer 2

我的方法是尝试为每个userId和userName计算一个未读计数和一个读计数。给定这4个计算列，您只需选择不同的 userId 即可优先选择未读计数为> 未读计数的行。如果MySql支持完全外部联接，则不会简化计算。这必须通过左右外部联接的联合来模拟：

SELECT DISTINCT userId, userName FROM (
        SELECT sq1.userId,
        sq1.userName,
        sq1.unreadCount,
        IFNULL(sq2.readCount,0) AS readCount FROM
            (SELECT userId, userName, count(*) AS unreadCount FROM msg
            WHERE msgStatus = 'unread'
            GROUP BY userId, userName) sq1
        LEFT JOIN
            (SELECT userId, userName, count(*) AS readCount FROM msg
            WHERE msgStatus = 'read'
            GROUP BY userId, userName) sq2
        ON sq1.userId = sq2.userId
    UNION
        SELECT sq2.userId,
        sq2.userName,
        IFNULL(sq1.unreadCount,0) AS unreadCount,
        sq2.readCount FROM
            (SELECT userId, userName, count(*) AS unreadCount FROM msg
            WHERE msgStatus = 'unread'
            GROUP BY userId, userName) sq1
        RIGHT JOIN
            (SELECT userId, userName, count(*) AS readCount FROM msg
            WHERE msgStatus = 'read'
            GROUP BY userId, userName) sq2
        ON sq1.userId = sq2.userId
) sq
ORDER BY IF(unreadCount > readCount, unreadCount, 0) DESC, userId
;

如何排序具有更多未读消息的用户，使其首先出现在mysql结果中

2 个答案: