Question

我想弄明白这一点，没有运气。我一直得到一些奇怪的结果！首先，我有一个包含一些行的MySQL数据库，结构如下所示，

ID MESSAGE_ID 信息时间 DATE

现在，message_id可以多次相同，这就是我的问题开始的地方。我想按ID选择dubplicated message_ID排序的最后一行。

所以，假设我有一个正常的get请求，结果看起来像这样，

Array
(
    [0] => Array
        (
            [id] => 3
            [message_id] => 1
            [from_user_id] => 3
            [to_user_id] => 1
            [message] => last
            [time_sent] => 1331874924
            [date_sent] => 16/03/2012
            [opened] => 0
            [ip] => ::1
            [deleted] => 0
            [reported] => 0
        )

    [1] => Array
        (
            [id] => 2
            [message_id] => 1
            [from_user_id] => 3
            [to_user_id] => 1
            [message] => middle
            [time_sent] => 1331874920
            [date_sent] => 16/03/2012
            [opened] => 0
            [ip] => ::1
            [deleted] => 0
            [reported] => 0
        )

    [2] => Array
        (
            [id] => 1
            [message_id] => 1
            [from_user_id] => 3
            [to_user_id] => 1
            [message] => first
            [time_sent] => 1331874916
            [date_sent] => 16/03/2012
            [opened] => 0
            [ip] => ::1
            [deleted] => 0
            [reported] => 0
        )

    [3] => Array
        (
            [id] => 4
            [message_id] => 2
            [from_user_id] => 3
            [to_user_id] => 1
            [message] => test
            [time_sent] => 1331874916
            [date_sent] => 16/03/2012
            [opened] => 0
            [ip] => ::1
            [deleted] => 0
            [reported] => 0
        )

)

现在，我想要的是删除dubplicated message_id并且只获取它（注意它应该如何按ID排序）

Array
(
    [0] => Array
        (
            [id] => 3
            [message_id] => 1
            [from_user_id] => 3
            [to_user_id] => 1
            [message] => last
            [time_sent] => 1331874924
            [date_sent] => 16/03/2012
            [opened] => 0
            [ip] => ::1
            [deleted] => 0
            [reported] => 0
        )

    [1] => Array
        (
            [id] => 4
            [message_id] => 2
            [from_user_id] => 3
            [to_user_id] => 1
            [message] => test
            [time_sent] => 1331874916
            [date_sent] => 16/03/2012
            [opened] => 0
            [ip] => ::1
            [deleted] => 0
            [reported] => 0
        )

)

我之前一直在尝试的是，

$this->db->order_by(‘id’, ‘DESC’);
$this->db->group_by(‘message_id’);

和

$this->db->group_by(‘message_id’);
$this->db->order_by(‘id’, ‘DESC’);

但是我没有得到message_id的最新结果，只有第一个（看起来它在删除之前没有找到或者什么？）

任何帮助都会很棒！

Answer 1

我在桌子上取得了成功：

select * from 
    (select * from da_user_messages order by id desc) t 
where receiver=1 group by msg_session

在你的情况下，msg_session是message_id，receiver是to_user_id，da_user_messages是你的表名。

group_by和order_by与codeigniter

1 个答案: