题解 | #统计每个用户的平均刷题数#
统计每个用户的平均刷题数
https://www.nowcoder.com/practice/f4714f7529404679b7f8909c96299ac4
select university, difficult_level, count(question_detail.question_id) / count(distinct user_profile.device_id) as 'avg_answer_cnt' from user_profile inner join question_practice_detail on user_profile.device_id = question_practice_detail.device_id inner join question_detail on question_detail.question_id = question_practice_detail.question_id group by university, difficult_level having university = '山东大学'
1、3表连接, 内连就行,没有null数据
2、按照学校和难度分组
3、平均刷题数: question_detail表中 题数 / user_profile表中 人数