题解 | #统计每个学校的答过题的用户的平均答题数#

select user_profile.university, count(question_practice_detail.question_id)/count(distinct question_practice_detail.device_id) as avg_answer_cnt
from user_profile
inner join question_practice_detail
on user_profile.device_id = question_practice_detail.device_id
group by user_profile.university 
order by user_profile.university asc