我试图从每次对话中获取最后一条消息，唯一的问题是我没有使用对话表。
我使用的是一个消息表，我的表列如下所示：
id from_id to_id text isread isseen created_at updated_at
现在我可以检索这样的对话：
$messages = Message::select('*')->
from(DB::raw("(select * from `messages` where `to_id` = ".Auth::id()." order by `created_at` desc) as sub"))->
groupBy('from_id')->orderBy('created_at', 'desc')->
paginate(7);
唯一的缺点是，我不会检索每次对话的最后一条消息，而是检索收到的最后一封消息。
如何检索每次对话的最后一条消息？
示例检索用户63个对话和每个对话的最后一条消息：
id from_id to_id text isread isseen created_at updated_at
23 224 63 a 0 0 2015-03-28 22:23:54 2015-03-28 22:23:54
20 63 225 b 0 0 2015-03-28 22:23:06 2015-03-28 22:23:06
16 225 63 hi 0 1 2015-03-28 22:21:32 2015-03-28 22:21:32
我想到了一个主意，但不确定：
$messages = Message::select('*')->
from(DB::raw("
(
(select *, to_id as theuser from `messages` where `to_id` = ".Auth::id()." order by `created_at` desc)
union
(select *, from_id as theuser from `messages` where `from_id` = ".Auth::id()." order by `created_at` desc) group by theuser
) as sub"))->
groupBy('from_id')->orderBy('created_at', 'desc')->
paginate(7);
这也必须有效：这种方法的不同之处在于，在max（）函数的帮助下实现了自联接，如下所示：
SELECT from_id, MAX(created_at) AS last FROM messages GROUP BY from_id
因此：
$pagedMessages = Message::select('*')->
from(
DB::raw("
messages AS m
JOIN (
SELECT from_id, MAX(created_at) AS lm FROM messages GROUP BY from_id
) AS lm
ON lm.from_id = m.from_id AND lm.created_at = m.created_at
"))->
paginate(7);
我自己找到了解决方案，谢谢大家！：）
$messages = Message::select('*')->
from(DB::raw("
(
SELECT *,`from_id` as `theuser`
FROM `messages` WHERE `to_id` = 63
union
SELECT *,`to_id` as `theuser`
FROM `messages` WHERE `from_id` = 63
order by `created_at` desc
) as `sub`"))->groupBy('theuser')->
orderBy('created_at', 'desc')->
paginate(7);