题解 | #浙大不同难度题目的正确率#

select qd.difficult_level difficult_level,count(qpd.result = "right" or null)/count(qpd.result) correct_rate
from question_practice_detail qpd
inner join (select device_id from user_profile where university = "浙江大学") up
on qpd.device_id = up.device_id
inner join question_detail qd
on qd.question_id = qpd.question_id
group by qd.difficult_level
order by correct_rate ASC