题解 | 浙大不同难度题目的正确率

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