题解 | 浙大不同难度题目的正确率

select 
    qd.difficult_level,
    sum(if(qp.result='right',1,0))/count(qp.result) as correct_rate
from
    user_profile as u
    left join question_practice_detail as qp
    on u.device_id=qp.device_id
    left join question_detail as qd
    on qp.question_id=qd.question_id
where
    university='浙江大学' and difficult_level is not null
group by 
        qd.difficult_level
order by 
        correct_rate