题解 | 浙大不同难度题目的正确率
select difficult_level,count(case when b.result='right' then 1 else null end )/count(b.question_id) correct_rate from user_profile a left join question_practice_detail b on a.device_id = b.device_id inner join question_detail c on b.question_id = c.question_id where a.university = '浙江大学' group by difficult_level order by correct_rate