题解 | #浙大不同难度题目的正确率#

select qd.difficult_level,sum(if(result = 'right',1,0))/count(qd.difficult_level) as correct_rate
from question_practice_detail pqd,question_detail qd
where pqd.question_id = qd.question_id and pqd.device_id in (select device_id from user_profile where university = '浙江大学')
group by qd.difficult_level
order by correct_rate