Question

我在分组时按ID排序结果时遇到一些问题：

$get_seen_messages = mysql_query("SELECT * 
                                  FROM chat 
                                  WHERE userto='$login_cookie' 
                                    AND status='seen' 
                                  GROUP BY userfrom 
                                  ORDER BY id DESC");

请帮帮我：D

Answer 1

哪个id？您应该从不使用SELECT *与GROUP BY。使用GROUP BY时，所有未加聚合的列都应位于GROUP BY中。所以，这是一个正确形成的查询

SELECT userfrom, MAX(id) as id
FROM chat
WHERE userto = '$login_cookie' AND status = 'seen'
GROUP BY userfrom
ORDER BY MAX(id) DESC;

我怀疑，您希望每个userfrom的聊天最新一行。在这种情况下，正确形成的查询如下所示：

select c.*
from chat c
where userto = '$login_cookie' and status = 'seen' and
      id = (select max(c2.id)
            from chat c2
            where c2.userto = c.userto and c2.status = c.status
           );

Answer 2

您是否尝试过subquerys？

$get_seen_messages = mysql_query("
    SELECT * FROM
        (SELECT * 
            FROM chat 
            WHERE userto='$login_cookie' 
            AND status='seen' 
            GROUP BY userfrom) as subquery 
    ORDER BY id DESC");

MySQL：按ID排序分组结果

2 个答案: