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,sum(if(result='right',1,0))/count(question_id) as correct_rate from question_practice_detail as a left join question_detail as b using(question_id) where a.device_id in (select device_id from user_profile where university='浙江大学' ) group by difficult_level order by correct_rate;
少用一次join
调试发现子查询多于一行,于是用in通过测试
不知道这样做好不好