题解 | #浙大不同难度题目的正确率#

1. 思路很简单
2. 首先把三个表外连接起来
3. 然后筛选出浙大的和困难等级不为空的(之前测试不懂为什么有空的)
4. 再根据困难等级分组
5. 最后算出对的次数与总数相除就是正确率了

difficult_level,
sum(if(result='right',1,0))/COUNT(*) as correct_rate
from user_profile
LEFT JOIN question_practice_detail USING(device_id)
LEFT JOIN question_detail using(question_id)
WHERE university = "浙江大学" and difficult_level is not null
GROUP BY difficult_level
ORDER BY correct_rate ASC