题解 | #浙大不同难度题目的正确率#
浙大不同难度题目的正确率
http://www.nowcoder.com/practice/d8a4f7b1ded04948b5435a45f03ead8c
知识点：left join
select
difficult_level,
avg(if(result='right',1,0)) as correct_rate
from (
select device_id
from user_profile
where university='浙江大学'
)a
left join question_practice_detail b
on a.device_id=b.device_id
left join question_detail c
on b.question_id=c.question_id
where difficult_level is not null
group by difficult_level
order by correct_rate
;
select
difficult_level,
avg(if(result='right',1,0)) as correct_rate
from (
select device_id
from user_profile
where university='浙江大学'
)a
left join question_practice_detail b
on a.device_id=b.device_id
left join question_detail c
on b.question_id=c.question_id
where difficult_level is not null
group by difficult_level
order by correct_rate
;
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