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
https://www.nowcoder.com/practice/5400df085a034f88b2e17941ab338ee8
select university, difficult_level, round(count(q.question_id)/count(distinct u.device_id),4) as avg_answer_cnt from user_profile as u inner join question_practice_detail as q on q.device_id = u.device_id inner join question_detail as qd on q.question_id = qd.question_id group by university,difficult_level
一开始就想的是用inner join,但是苦于不知道怎么写,以为需要重新选择交集表再写一次,看了答案才知道,可以连着写inner join,不需要再选择一次对应表列