题解 | #浙大不同难度题目的正确率#
浙大不同难度题目的正确率
https://www.nowcoder.com/practice/d8a4f7b1ded04948b5435a45f03ead8c
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
join question_practice_detail as qpd
on up.device_id=qpd.device_id
join question_detail as qd
on qpd.question_id=qd.question_id
where university='浙江大学'
group by difficult_level
#这样group by difficult_level having university='浙江大学'的话会编译错误出错，应当用下面的：
#group by university,difficult_level having university="浙江大学"
order by correct_rate
