题解 | #浙大不同难度题目的正确率#

select 
    difficult_level,
    avg(if(result='right',1,0)) as correct_rate
from (select    
    b.device_id,b.question_id,b.result,
    c.difficult_level
from
    (
        select
            device_id,
            question_id,
            result
        from
            question_practice_detail
    ) b
    join question_detail c on b.question_id = c.question_id 
    join user_profile a on b.device_id = a.device_id and university = '浙江大学') p group by difficult_level order by correct_rate;

用了两次子查询 可能有点儿麻烦

select 之后加distinct会报错 不知道为什么