题解 | #浙大不同难度题目的正确率#

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