题解 | #统计每个学校的答过题的用户的平均答题数#

select
    T1.university,
    (
        count(T2.question_id) / count(distinct T2.device_id)
    ) as avg_each_q
from
    user_profile T1,
    question_practice_detail T2
where
    T1.device_id = T2.device_id
group by
    university;

Mark一下。