题解 | #异常的邮件概率#
异常的邮件概率
https://www.nowcoder.com/practice/d6dd656483b545159d3aa89b4c26004e
select date, round(sum(case when type = 'no_completed' then 1 else 0 end) / count(*), 3) p from email where send_id NOT in (select id from user where is_blacklist = 1) and receive_id NOT in (select id from user where is_blacklist = 1) group by date
这题的重点在于sum(case when type = 'no_completed' then 1 else 0 end) / count(*)， case when 和 sum 函数累加发送失败的次数。
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