题解 | 统计每个用户的平均刷题数

--最终表格展示选项
select up.university, qd.difficult_level,
--与之前题目/去重后的device_id不一样，本题应该使用去重后的difficult_level,别忘记加上 as
round(count(qpd.question_id)/count(distinct qd.difficult_level), 4) as avg_answer_cnt
from question_practice_detail as qpd
join user_profile as up on up.device_id = qpd.device_id
join question_detail as qd on qd.question_id = qpd.question_id
where up.university = '山东大学'
group by up.university, qd.difficult_level;