题解 | #浙大不同难度题目的正确率#

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