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,round(count(b.question_id)/count(distinct(b.device_id)),4) avg_answer_cnt from user_profile a right join question_practice_detail b on a.device_id = b.device_id right join question_detail c on b.question_id = c.question_id group by university,difficult_level having university = '山东大学'
总结错误：
在group by中没有加university字段导致报错
group by中出现的字段一定要出现在select中
