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(difficult_level)/count(distinct t1.device_id) as avg_answer_cnt from question_practice_detail t1 join user_profile t2 on t1.device_id=t2.device_id join question_detail t3 on t1.question_id=t3.question_id where university='山东大学' group by difficult_level ;
参照上一题,微调count(),group by,以及增加where条件查询即可。