如何计算每个关注者的二级追随者？

Question

我想知道二级追随者是什么意思？我有一个表，下面有两列: followee和followers

Followee Follower
A        B
B        C
B        D
B        E
A        F
F        G
F        H
B        H

找出二级追随者是什么？

Answer 1

为了详细说明我的评论，您可以使用self join来查看这一点。

declare @table table(Followee char(1), Follower char(1))
insert into @table
values
('A','B'),
('B','C'),
('B','D'),
('B','E'),
('A','F'),
('F','G'),
('F','H'),
('B','H')

select 
    l.Followee
    ,f.Follower as SecondDegreeFollower
    ,count(*) as CT
from
    @table l
left join
    @table f on f.Followee = l.Follower
where
    f.Follower is not null
group by
    l.Followee
    ,f.Follower

返回

+----------+----------------------+----+
| Followee | SecondDegreeFollower | CT |
+----------+----------------------+----+
| A        | C                    |  1 |
| A        | D                    |  1 |
| A        | E                    |  1 |
| A        | G                    |  1 |
| A        | H                    |  2 |
+----------+----------------------+----+