题解 | 浙大不同难度题目的正确率

select
   
difficult_level,count(case when b.result='right' then 1 else null end )/count(b.question_id) correct_rate
from
    user_profile a
    left join question_practice_detail b on a.device_id = b.device_id
    inner join question_detail c on b.question_id = c.question_id
where
    a.university = '浙江大学' 
group by difficult_level
order by correct_rate