题解 | 浙大不同难度题目的正确率

select
    qd.difficult_level as diffcult_level,
    sum(
        case
            when qp.result = 'right' then 1
            else 0
        end
    ) / count(qp.question_id) as correct_rate
from
    user_profile u
    inner join question_practice_detail qp on u.device_id = qp.device_id
    inner join question_detail qd on qp.question_id = qd.question_id
where
    u.university = '浙江大学'
group by
    qd.difficult_level
order by correct_rate