题解 | #统计每个用户的平均刷题数#

select up.university,qd.difficult_level,
round(count(qpd.question_id)/count(distinct qpd.device_id),4) as avg_answer_cn##使用distinct为关键
from question_practice_detail qpd
join user_profile as up
on qpd.device_id =up.device_id and up.university='山东大学'
join question_detail qd
on qpd.question_id	=qd.question_id	
group by up.university,qd.difficult_level