题解 | #浙大不同难度题目的正确率#

#浙江大学(where)的用户在不同难度题目(group by)下答题的正确率情况
select qd.difficult_level,sum(if(q.result='right',1,0))/count(question_id) correct_rate
from question_practice_detail q
inner join user_profile
using(device_id)
inner join question_detail qd
using(question_id)
where university='浙江大学'
group by difficult_level
order by correct_rate;

tips:要根据题目所给的语句逐步分析用什么函数