题解 | #浙大不同难度题目的正确率#

select difficult_level,
#avg(if(qpd.result = 'right', 1, 0)) as correct_rate
#sum(if(qpd.result = 'right', 1, 0)) / count(qpd.question_id) as correct_rate
count(if(qpd.result = 'right', 1, null)) / count(qpd.question_id) as correct_rate
from user_profile as up

inner join question_practice_detail as qpd
on up.device_id = qpd.device_id

inner join question_detail as qd 
on qd.question_id = qpd.question_id

where up.university = '浙江大学'
group by qd.difficult_level
order by correct_rate asc