题解 | #牛客每个人最近的登录日期(三)#

#分子：login自连接，h1的date和h2的date差一天，h2的date作为后一天，若h2的date不为null，说明后一天有登录，计算h2不为null的user_id个数
# 分母：所有的user_id个数

select 
round(
    (select count(distinct user_id)
    from
    (
    select h1.user_id,h1.date,h2.date as dt2
    from login h1
    left join login h2 
    on h1.user_id=h2.user_id and date_add(h1.date,interval 1 day)=h2.date)h
    where dt2 is not null)
 /(select count(distinct user_id) from login),
 3)