题解 | #浙大不同难度题目的正确率#

select qd.difficult_level,
    count(
        CASE
            WHEN qpd.result = 'right' THEN 1
        END
    )/count(qpd.question_id) as correct_rate
from 
    question_practice_detail qpd
join
    question_detail qd
on qpd.question_id = qd.question_id
join
    user_profile u
on u.device_id = qpd.device_id
where 
    u.university = "浙江大学"
group by
    qd.difficult_level
order by 
    correct_rate