题解 | 统计每个用户的平均刷题数

这题比较简单，就是在上一题的基础上，加上分组查询条件，限定山东大学即可，考察的是分组过滤having的使用
select  
up.university,
qd.difficult_level,
round(count(qpd.question_id)/count(distinct qpd.device_id),4) as avg_answer_cnt
from question_practice_detail as qpd
join question_detail as qd on qpd.question_id = qd.question_id
join user_profile as up on up.device_id=qpd.device_id
group by up.university,qd.difficult_level
having up.university='山东大学'
order by up.university,qd.difficult_level;