SQL题：浙大不同难度题目的正确率
这道题的话我本是这么做的 虽然看上去很麻烦 但是为什么计算出来是1呢
描述
题目：
现在运营想要了解浙江大学的用户在不同难度题目下答题的正确率情况，请取出相应数据，并按照准确率升序输出。
(select *
from user_profile
where university='浙江大学') as tt
#答题正确率为 正确数/总答题数 或总题数
#不同难度 group by difficult_level
#提取出浙大的正确数
(select question_id
from question_practice_detail,user_profile
where user_profile.device_id=question_practice_detail.device_id and university='浙江大学' and result='right') as pp
//完整代码
select difficult_level,count(pp.question_id)/count(tt.question_id) as correct_rate
from user_profile,
(select question_id
from user_profile,question_practice_detail
where user_profile.device_id=question_practice_detail.device_id and university='浙江大学'
) as tt,
(select question_id
from question_practice_detail,user_profile
where user_profile.device_id=question_practice_detail.device_id
and university='浙江大学' and result='right') as pp
where question_detail.question_id=tt.question_id
group by difficult_level
order by difficult_level asc;
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