题解 | #统计每个用户的平均刷题数#

select university, 
difficult_level, 
round(count(qpd.question_id) / count(distinct qpd.device_id),4) as avg_answer_cnt
from question_practice_detail as qpd
inner join user_profile as up
on qpd.device_id = up.device_id
inner join question_detail as qd
on qpd.question_id = qd.question_id
group by university, difficult_level
having university = '山东大学'

最后条件选择用having