题解 | #浙大不同难度题目的正确率#

select t3.difficult_level,
    round(sum(if(t2.result='right',1,0))/count(t2.question_id),4) as correct_rate
from  user_profile t1,question_practice_detail t2,question_detail t3
where t1.device_id = t2.device_id and t2.question_id = t3.question_id and t1.university='浙江大学'
group by t3.difficult_level
order by correct_rate asc