问个 SQL 查询语句问题

不是那种点击进入聊天界面那种获取聊天记录 是相当于我的聊天信息那种 排列一堆和我聊过天的人的列表

mark 一下看答案。只用一条 sql......

首先假设你这个需求是做一个类似论坛的消息中心，不是实时会话 IM，而且必须存数据库

简单来说加个会话表，用这个会话表排序分页，message 表关联到这个会话表去，每次有新消息了更新下会话表的时间

不是很明白什么意思, 这样么?
````sql
select a.receive_id, a.send_id, a.is_read, a.ctime
from message a
join (select receive_id, send_id
from message
where (receive_id = userid or send_id = userid)
order by ctime desc
limit 1) b on b.receive_id = a.receive_id and b.send_id = a.send_id
order by ctime desc;
````

@refear99 噢！这样好像是简单点 那感觉也不需要关联呀 直接会话表存那个好了。

@luguhu 哇 好复杂 我也不太懂 我来测试测试

@luguhu 好像不对

select * from message
order by (
select max(ctime) from message m2
where message.send_id = m2.send_id
) desc

@qwertyzzz 应该是我理解错了, 你是想获取每个对话的第一条吗?

没懂，是不是这样？

SELECT *
FROM message
WHERE
`receive_id` =:id
OR
`send_id` =:id
ORDER BY `ctime` DESC
limit :page,:count;
[ 'id'=>id,'page'=>page,'count'=>count ]

用 window 函数为每一行编号就好做了

select *
from (
select receive_id, send_id, is_read, ctime
from (
select *, row_number() over(PARTITION BY receive_id, send_id order by ctime desc)
from (
select * from message where receive_id = <userId> or send_id = <userId>
) as t
) as t
where row_number = 1
) as t
limit 20

感觉 row_number over partition by 很容易就搞定了， 没有 row number 就难搞了

select myid,uid,max(ctime+is_read+soRr) as data
from (
select send_id,receive_id,is_read,ctime,'send' as sORr
where send_id='myid'
union all
select receive_id,send_id,is_read,ctime,'recv' as sORr
where receive_id='myid'
)
group by myid,uid
order by data desc

。。。。。这样写是不是很皮，难得我还特意登一下 PC 网页
关于分页性能问题。既然都要在消息列表里找了，还管那些干啥。。。。。。。。

其实应该用关联子查询。

看到这个功能,觉得有点意思,就动手建表写 sql,花了不少时间,已经正常返回结果:
获取步骤:
1)查询每个不同接收者最新的一条数据;
2)查询每个不同发送者最新的一条数据;
3)查询接收者 /发送者最新的一条数据,并将非本人 id 存放到 other_id;
4)去除重复的 other_id;
5)获取每一条完整的数据,并进行倒序,分页
使用的是 mysql:
select m1.id,m1.receive_id,m1.send_id,m1.content,m1.ctime from message as m1
join
(
select a.*,max(a.max_ctime) as a_ctime from (
(select receive_id as other_id, receive_id,send_id,max(ctime) as max_ctime from message where receive_id<>'userid' and send_id='userid' group by receive_id )
union
(select send_id as other_id, receive_id,send_id,max(ctime) as max_ctime from message where send_id<>'userid' and receive_id='userid' group by send_id )
) as a group by a.other_id
) as m2
on m1.receive_id=m2.receive_id and m1.send_id=m2.send_id and m1.ctime=m2.a_ctime
order by m1.ctime desc limit 0,20;

@james2013 哇 感觉好复杂的样子 我按楼上的加了一个表 然后发信息的时候更新 倒是可以了。