sum(if(q1.result='right',1,0))/count(q1.question_id) as correct_rate
from question_detail q
left join question_practice_detail q1
on q.question_id=q1.question_id
left join user_profile u
on q1.device_id=u.device_id
where u.university='浙江大学'
group by 1
order by 2;

解题思路：1⃣️多表连接

2⃣️正确率的计算公式：回答正确的个数/回答的总题目