题解 | #浙大不同难度题目的正确率#

select difficult_level,
sum(if(result='right',1,0))/sum(if (result is not null,1,0)) as correct_rate
from
    (select 
    u.university,
    qpd.result,
    qd.difficult_level
    from user_profile u
    join  question_practice_detail qpd
    on u.device_id=qpd.device_id
    join question_detail qd
    on qpd.question_id=qd.question_id
    where university='浙江大学') as t

group by difficult_level
order by correct_rate asc;