Question

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

如何在这种情况下查询“A”的2级关注者的数量是多少？

Answer 1

我认为这很容易

select count(distinct t1.Follower) 
    from t 
       join 
         t t1 
       on t.Follower=t1.Followee
  where t.Followee='A'

Answer 2

让表的名称为“follow”。找到第二学位的粉丝是“A”：

select count(follower) from follows 
where followee in 
(select distinct follower from follows where followee='A')

如果你想找到所有被跟随者的第二学位追随者数量：

select f2.followee, count(f1.follower) 
from follows f1 inner join follows f2 
on f2.follower=f1.followee 
group by f2.followee

Answer 3

select a.followee,count(DISTINCT a.followee,b.follower) from following a
left join following b
on b.followee = a.follower
left join following d
on d.followee = a.followee and d.follower = b.follower
where d.followee is null
GROUP BY a.followee

Answer 4

假设表的名称为tbl。

SELECT count (distinct tbl.follower) 
FROM tbl 
JOIN 
(SELECT distinct follower FROM tbl WHERE followee = 'A') AS tbl2
ON tbl.followee = tbl2.follower

答案是5。

如何在数据库中查找二度关注者的数量如下？

4 个答案: