题解 | #浙大不同难度题目的正确率#

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