题解 | #统计每个学校各难度的用户平均刷题数#
统计每个学校各难度的用户平均刷题数
http://www.nowcoder.com/practice/5400df085a034f88b2e17941ab338ee8
select t1.university,t3.difficult_level,
round(count(1)/count(distinct t1.device_id),4) as avg_answer_cnt
from user_profile t1
join question_practice_detail t2 on t1.device_id = t2.device_id
join question_detail t3 on t2.question_id = t3.question_id
group by university,difficult_level
