题解 | #浙大不同难度题目的正确率#

#1.浙江大学 university = '浙江大学'
#2.不同难度 group by difficult_level
#3.答题正确率 sum(if(result='right',1,0)) / count(qpd.question_id)
#4.联合表 inner join和left join和right join的区别
select 
    difficult_level,
    sum(if(result='right',1,0)) / 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 qpd.question_id = qd.question_id and university = '浙江大学'
group by difficult_level
order by correct_rate

#1.浙江大学 university = '浙江大学'

#2.不同难度 group by difficult_level

#3.答题正确率 sum(if(result='right',1,0)) / count(qpd.question_id)

#4.联合表 inner join和left join和right join的区别：

http://www.learnfk.com/mysql/mysql-join.html