题解 | 异常的邮件概率

select
    date,
    round(avg(type = 'no_completed'), 3) as 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
order by date asc

avg(type = 'no_completed')等同于sum(if(type = 'no_completed', 1, 0))/count(*)