题解 | 浙大不同难度题目的正确率

select
    difficult_level,
    sum(result = 'right') / count(*) correct_rate
from
    user_profile up
    join question_practice_detail qpd on up.device_id = qpd.device_id
    join question_detail qd on qpd.question_id = qd.question_id
where university = '浙江大学'
group by difficult_level
order by correct_rate asc