题解 | 浙大不同难度题目的正确率

select 
    difficult_level,
    (
        sum(
        case when result='right' then 1
        else 0
        end
        )
    )/count(result) as correct_rate
    
from
    (
    select
      difficult_level,result
    from user_profile up
    left join question_practice_detail qpd
    on up.device_id=qpd.device_id
    inner join question_detail qd
    on qpd.question_id=qd.question_id
    where up.university='浙江大学'
    ) as a
group by difficult_level
order by correct_rate
;