题解 | 不用join也能解
异常的邮件概率
https://www.nowcoder.com/practice/d6dd656483b545159d3aa89b4c26004e
select
date,
round(count(case when type='no_completed' then id else null end )/count(distinct id),3)as P
from email
where send_id in (select distinct id from user where is_blacklist=0)
and receive_id in (select distinct id from user where is_blacklist=0)
group by date
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