题解 | #浙大不同难度题目的正确率#

select qd.difficult_level,sum(if(qpd.result='right',1,0))/count(qpd.question_id) as correct_rate
from user_profile as up 
inner join question_practice_detail as qpd
on up.device_id=qpd.device_id and university='浙江大学'
inner join question_detail as qd
on qpd.question_id=qd.question_id
group by difficult_level
order by correct_rate asc