题解 | 统计每个学校的答过题的用户的平均答题数

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