题解 | 浙大不同难度题目的正确率

select t.difficult_level,
    round(sum(if(result="right",1,0)) / sum(if(result is not null,1,0)),4) as correct_rate
from user_profile p
    right join question_practice_detail q
    on p.device_id = q.device_id
    left join question_detail t
    on q.question_id = t.question_id
where university = "浙江大学"
group by t.difficult_level
order by correct_rate ;