题解 | #统计每个学校的答过题的用户的平均答题数#

select
    university,round(count(question_id)/count(distinct q.device_id),4)avg_answer_cnt
from 
    question_practice_detail q
inner join
    user_profile u
on
    q.device_id = u.device_id
group by
    university
order by 
    university