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
http://www.nowcoder.com/practice/d8a4f7b1ded04948b5435a45f03ead8c
直接用平均就可以求出占比,外键同名可以直接用using,无需重命表名,这样不用处理字段重名
select difficult_level, avg(if(result='right',1,0)) correct_rate from user_profile left join question_practice_detail using(device_id) join question_detail using(question_id) where university='浙江大学' group by difficult_level order by correct_rate