题解 | 浙大不同难度题目的正确率

select
    n1.difficult_level,
    avg(if(n1.result='right',1,0)) as correct_rate
from
    user_profile up
    left join (
        select
            device_id,
            result,
            difficult_level
        from
            question_practice_detail qpd
            join question_detail qd on qpd.question_id = qd.question_id
    ) as n1 on n1.device_id = up.device_id
where
    up.university = '浙江大学' and n1.difficult_level is not null
group by n1.difficult_level
order by correct_rate;