题解 | #浙大不同难度题目的正确率#

select qd.difficult_level as difficult_level ,
count(if(qpd.result='right',1,NULL))/count(qd.question_id) as correct_rate
from question_practice_detail as qpd 
inner join (
    select up.device_id,up.university
    from user_profile AS up
    where up.university='浙江大学'
) as tmp
on tmp.device_id=qpd.device_id
left join
  question_detail as qd
on qpd.question_id=qd.question_id

group by qd.difficult_level
order by correct_rate ASC;