mysql - Mysql通过某个字段计算带有组的计数（*）的中间值

Question

我有这个查询：

select count(*) from logins group by user_id

这将返回每个用户的用户登录号：

数数（*）

---

10

23

35

54

使用单一且高效的查询，如何选择（计算）这个的中间值？中等 = (10+23+35+54)/4。

Answer 1

select avg(num_login) 
  from (select count(*) as num_login 
  from logins group by user_id) as num_logins 

Answer 2

select avg(count(*)) from logins group by user_id

Answer 3

SELECT AVG(c) FROM (SELECT COUNT(*) AS c FROM logins GROUP BY user_id) AS v

这有效..

Answer 4

使用子查询，然后AVG对子查询的结果起作用：

SELECT AVG(logins_cnt) AS logins_cnt
FROM   (SELECT COUNT(1) AS logins_cnt
        FROM logins 
        GROUP BY user_id
       ) a;

Answer 5

你试过平均功能吗？

select avg(select count(*) from logins group by user_id)