题解 | #浙大不同难度题目的正确率#

select difficult_level, sum(if(result='right',1,0))/count(result) as correct_rate 
from question_practice_detail A 
join user_profile B on A.device_id = B.device_id and university='浙江大学' 
join question_detail C on A.question_id = C.question_id
group by difficult_level
order by correct_rate;

问题分解：

限定条件：where university='浙江大学'

按照问题难易程度分组，group by difficult_level

sum(if(result='right',1,0))/count(result),求出正确率

表链接。question_practice_detail A join user_profile B on A.device_id = B.device_id and university='浙江大学' ,然后再 left join question_detail C on B.question_id = C.question_id

细节问题：

as

完整代码：

select difficult_level, sum(if(result='right',1,0))/count(result) as correct_rate

from question_practice_detail A

join user_profile B on A.device_id = B.device_id and university='浙江大学'

left join question_detail C on A.question_id = C.question_id

group by difficult_level

order by correct_rate;