题解 | 浙大不同难度题目的正确率

这道题比前一个更复杂一点，计算难度增加了，不仅得计算正确数，还得计算准确率=正确数/总回答数

select qd.difficult_level,
sum(case
	when qpd.result='right' then 1 else 0 end)/count(*) as correct_rate
from question_practice_detail as qpd
left join question_detail as qd
on qpd.question_id=qd.question_id
join user_profile as up
on qpd.device_id=up.device_id and up.university='浙江大学'
group by qd.difficult_level
order by correct_rate;