如何在sql中获取计数列的平均值

Question

select count(user_id) 
from photos 
group by user_id ;
4
3
1
2
1
1
12
5
1
4
8
2
1
4
5
2
1
2
1
1
3
5
4
4
5
1
3
5
5
1
1
8
10
2
1
2
4
5
5
3
1
1
5
1
6
5
1
2
2
2
9
4
11
3
2
1
2
3
2
1
3
2

select avg(count(user_id)) 
from photos 
group by user_id;

错误代码：1111。无效使用组功能

如何获得此列的平均值

Answer 1

您想要整个聚合表的平均值吗？

SELECT AVG(cnt) AS avg_cnt
FROM
(
SELECT COUNT(user_id) AS cnt 
FROM photos
GROUP BY user_id
) t;

Answer 2

我想应该是这样的：

select sum(column1)/(select count(*) from  photos) from photos ;