题解 | 浙大不同难度题目的正确率

select d.difficult_level 'difficult_level', round(sum(case when q.result='right' then 1 else 0 end)/count(q.question_id),4) 'correct_rate'
from question_detail d ,user_profile u,question_practice_detail q
where u.device_id=q.device_id and q.question_id=d.question_id and u.university='浙江大学'
group by d.difficult_level
order by correct_rate asc;

主要是正确率计算部分：答题对的数量/答题总次数