题解 | 浙大不同难度题目的正确率

select
    difficult_level,
    sum(
        case
            when result = 'right' then 1
            else 0
        end
    ) / count(q1.question_id) as correct_rate
from
    user_profile u
    join question_practice_detail q on q.device_id = u.device_id
    join question_detail q1 on q1.question_id = q.question_id
where
    u.university = '浙江大学'
group by
    difficult_level
order by sum(
        case
            when result = 'right' then 1
            else 0
        end
    ) / count(q1.question_id) 
;