题解 | #浙大不同难度题目的正确率#

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