Question

这是两个表：

1.user
user_id  |  full_name   | username
1              A             A_1
2              B             B_2
3              C             C_3
4              D             D_4
5              E             E_5

2.user_follower
user_id  |  follower_id  |  follow_dtm
2              4            2018-10-09 10:10:10
2              3            2018-01-09 11:10:10
1              5            2018-11-09 07:10:10
4              2            2018-10-09 06:10:10
4              5            2018-10-09 00:10:10

用户的关注者：2 输出应为：

user_id: 4  fullname: D username: D_4  f_total_flwr: 2 (num of flwr of id-4)  following: yes
user_id: 3  fullname: C username: C_3  f_total_flwr: 0 (num of flwr of id-3)  following: no

我需要一个mysql查询，以从user表中找到特定用户的所有关注者以及关注者的详细信息，并且需要知道每个关注者拥有的关注者的数量，我还需要了解特定的关注者用户还关注该关注者。这是我尝试过的：

SELECT u.user_id 
     , u.full_name
     , u.username
     , COUNT(DISTINCT uf.follower_id) f_total_flwr
     , case when b.user_id is null then 'no' else 'yes' end following 
  FROM user_follower
  JOIN user u 
    ON user_follower.follower_id = u.user_id
  LEFT 
  JOIN user_follower uf 
    ON u.user_id = uf.user_id
  LEFT 
  JOIN user_follower b 
    ON b.user_id = user_follower.follower_id 
   and b.user_id = u.user_id 
 WHERE user_follower.user_id=2 
 GROUP 
    BY u.user_id 
 ORDER 
    BY uf.follow_dtm DESC 
 LIMIT 30

我知道我正在接近;）。问题是，即使用户没有追随，我仍在使用following值来获取yes。这是另一件事-not all但some of them显示{{ 1}}应该是yes。谢谢！

Answer 1

尝试一下：

select u2.*,b.fcount, case when uf3.user_id is null then 'no' else 'yes' end as connected from user u2 inner join
(
select u.user_id,count(distinct(uf2.follower_id)) fcount
from user u 
inner join user_follower uf1 on u.user_id=uf1.follower_id and uf1.user_id=1
left join user_follower uf2 on uf2.user_id=uf1.follower_id
group by u.user_id
) b on u2.user_id=b.user_id
left join user_follower uf3 on u2.user_id=uf3.user_id and uf3.follower_id=1

我使用以下数据集进行了尝试：

USER

1，a，abcd

2，b，bcde

3，c，cdef

user_follower

1,2,10

1,3,11

2,3,10

3,1,13

并获得了预期的结果：

2，b，bcde，1，no

3，c，cdef，1，是

MySQL查询，用于查找关注者并关注

1 个答案: