题解 | #浙大不同难度题目的正确率#

select difficult_level,correct_rate
from (select university,difficult_level,sum(score)/count(result) as correct_rate
from (select a.device_id,university,result,difficult_level,
case when result='right' then 1 else 0 end as score
from user_profile as a,
question_practice_detail as b,
question_detail as c
where a.device_id=b.device_id
and b.question_id=c.question_id) as d
group by university,difficult_level) as e
where university='浙江大学'
order by correct_rate