Question

我有一个包含3个表的MySQL数据库：users，posts和users_posts。 users-posts关系是多对多的。如何获得所有帖子对的列表以及他们共有多少用户？它基本上给了我一个帖子列表以及有多少用户评论了它们。关键是要准备好数据导入网络分析软件。结果列表在网络术语中称为“边缘列表”，共同的用户是边缘权重。

架构：

users
id
name

posts
id
title
body

users_posts
user_id
post_id

期望的输出：

postname1         postname2     users_in_common
Here's a title    Title #2      2
Another post      Title #2      11

我尝试过搜索，但在多对多，加入，三张桌子，数量，对，共享等方面甚至都不知道正确的搜索字词。感谢您的帮助！

Answer 1

我的查询会生成所有帖子对，包括没有普通用户的帖子（在这种情况下，0中会有users_in_common）。在SQL Fiddle上尝试我的解决方案或查看代码：

select
    p1.title as postname1,
    p2.title as postname2,
    coalesce(s.users_in_common, 0) as users_in_common
from posts p1
    inner join posts p2 on p1.id < p2.id
    left join (
        select
            up1.post_id as post1_id,
            up2.post_id as post2_id,
            count(*) as users_in_common
        from users_posts up1, users_posts up2
        where up1.user_id = up2.user_id
            and up1.post_id < up2.post_id
        group by up1.post_id, up2.post_id
    ) s
    on (s.post1_id = p1.id and s.post2_id = p2.id)
order by p1.id, p2.id;

Answer 2

试试这个

select
  p1.title as postname1,
  p2.title as postname2,
  (select count(*) from user_posts up where up.post_id in (p1.post_id, p2.post_id) as users_in_common
from
  posts p1, posts p2

MySQL通过多对多的关系统计用户之间的共同点

2 个答案: