题解 | #浙大不同难度题目的正确率#

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