题解 | #浙大不同难度题目的正确率#

select
    difficult_level,
    sum(if (result = 'right', 1, 0)) / count(qd.difficult_level) as correct_rate
from
    question_practice_detail as qpd
    right join(
        select
            university,
            device_id
        from user_profile
        where university='浙江大学'
    )as up
    on qpd.device_id = up.device_id
    left join question_detail as qd on qpd.question_id = qd.question_id

group by
    difficult_level
having qd.difficult_level !='None'
order by correct_rate