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(qpd.question_id) as correct_rate
from user_profile as up
left join question_practice_detail as qpd
on up.device_id=qpd.device_id
left join question_detail as qd
on qpd.question_id=qd.question_id
where up.university = '浙江大学'
group by qd.difficult_level
having qd.difficult_level !='None' 
order by correct_rate asc