Question

我真的很感激任何试图简化MySQL查询的帮助。查询的目的是从消息表（users_messages）中检索消息，消息表包含以下列：message_id，from_id，to_id，message_content，date_sent。

from_id和to_id需要加入具有以下列的用户表（用户）：user_id，user_username。

另外我应该提一下，有一个被阻止的用户表（users_blocked），如果此表中有user_id功能，它会过滤掉任何消息。

所有这一切都很好，消息按照最新的第一个订购，这就是我想要的。我唯一的问题是它没有拉动相应的'message_content'。即它正在拉最近的日期，但不是最近的消息。

也许我需要一种不同的方法（例如子查询），但我无法理解它。

以下是查询：

select m.message_content,
    if(from_id < to_id, concat(from_id,to_id), concat(to_id,from_id)) as ft,
    if (from_id = $my_id, to_id, from_id) as other_id,
    max(date_sent) as most_recent
from users_messages m
    left join users_blocked ub1 on (from_id = ub1.blocked_id and ub1.user_id = $my_id)
    left join users_blocked ub2 on (to_id = ub2.blocked_id and ub2.user_id = $my_id)
where
    (from_id = $my_id or to_id = $my_id)
    and ub1.blocked_id is null
    and ub2.blocked_id is null
group by
    ft
order by
    most_recent desc

对不起，这是表结构：

用户

user_id    user_username
1          Simon
2          Amber
3          Tom

users_messages

message_id    from_id    to_id    date_sent             message_content
1             1          2        2012-07-04 11:52:12   Hello
2             1          2        2012-07-04 12:32:24   Another message
3             1          2        2012-07-04 14:00:00   Hello again

users_blocked

user_id    blocked_id
1          3

Answer 1

尝试：

select m.message_content,
       x.ft,
       x.other_id,
       x.most_recent
from (select if(from_id < to_id, concat(from_id,to_id), concat(to_id,from_id)) as ft,
             if(from_id = $my_id, to_id, from_id) as other_id,
             max(date_sent) as most_recent
      from users_messages um
      left join users_blocked ub1 
        on (um.from_id = ub1.blocked_id and ub1.user_id = $my_id)
      left join users_blocked ub2 
        on (um.to_id = ub2.blocked_id and ub2.user_id = $my_id)
      where ub1.blocked_id is null and ub2.blocked_id is null and
            (um.from_id = $my_id or um.to_id = $my_id)
      group by ft) x
join users_messages m
     on m.date_sent = x.most_recent and 
        m.from_id in ($my_id, x.other_id) and 
        m.to_id in ($my_id, x.other_id)
order by
    x.most_recent desc

SQLFiddle here。

Answer 2

这里我假设SimonKing想要来自users_messages表的消息内容，其中包括以下条件，

用户不应阻止任何一个方向，
用户之间传输的最新消息

这样，我修改了Mark Bannister查询如下，

SELECT temp.* FROM  (
SELECT um.*, concat(um.from_id,to_id) as direction FROM userMessages um
LEFT JOIN userBlocked ub1 ON um.from_id = ub1.user_id AND um.to_id = ub1.blocked_id
LEFT JOIN userBlocked ub2 ON um.to_id = ub2.user_id AND um.from_id = ub2.blocked_id 
WHERE ub1.user_id is null AND ub1.blocked_id is null AND ub2.user_id is null AND ub2.blocked_id is null
ORDER BY um.date_sent DESC
) temp
GROUP BY direction

SQL小提琴是http://sqlfiddle.com/#!2/bdc77/1/0

Answer 3

据我所知，此请求的主要问题是结果只包含第一个日期，而不包含消息。要解决此问题，您可以执行此操作：

制作具有最新日期的准备数据集：

选择to_id，from_id，max（date_sent）作为most_recent 来自users_messages m 在ub.user_id = $ my_id上左连接users_blocked ub 和（to_id，from_id）中的ub.blocked_id 哪里（from_id = $ my_id或to_id = $ my_id）和ub.blocked_id为空通过...分组 to_id，from_id 订购 most_recent desc

我看到你通过两个字段to_id，from_id来搜索数据。这个子查询不是计算诸如此类事物的最佳位置：

if(from_id < to_id, concat(from_id,to_id), concat(to_id,from_id)) as ft

然后只需从users_messages中选择其他所需数据，这些数据与我们的to_id，from_id和recent_date相匹配，来自准备好的表：

从

中选择嗯。*

(
select to_id, from_id, max(date_sent) as most_recent
from users_messages m
left join users_blocked ub on ub.user_id = 1
and ub.blocked_id in (to_id, from_id)
where
(from_id = 1 or to_id = 1)
and ub.blocked_id is null
group by
to_id, from_id
order by
most_recent desc
) as prepared_messages
left join users_messages um on um.from_id = prepared_messages.from_id
and um.to_id = prepared_messages.to_id
and um.date_sent = prepared_messages.most_recent

试图简化MySQL查询

3 个答案: