题解 | #浙大不同难度题目的正确率#

select difficult_level,sum(if(result='right',1,0))/count(question_id) correct_rate
from (select u.device_id,u.university,q.question_id,q.result,d.difficult_level
from user_profile u
join question_practice_detail q
on u.device_id=q.device_id
join question_detail d
on d.question_id=q.question_id
where university='浙江大学')aa
group by difficult_level
order by correct_rate