每日一刷：java基础+sql

Posted 2022-12-03 ！0 ！

java基础

题解：JAVA中是用final

题解：没有用break，所以会一直执行

题解：A、循环语句才会一直执行

题解：threadlocalmap使用开放定址法解决haah冲突，hashmap使用链地址法解决hash冲突

sql语句

SQL67：牛客每个人最近的登录日期(二)

select u.name,c.name,l.date
from login l
join user u
on l.user_id = u.id
join client c
on l.client_id = c.id
where (l.user_id,l.date) in (
    select user_id, max(date) 
    from login 
    group by login.user_id
)
order by u.name;

SQL68：牛客每个人最近的登录日期(三)

select 
round(count(distinct user_id)*1.0/(select count(distinct user_id) from login) ,3)
from login
where (user_id,date)
in (select user_id,DATE_ADD(min(date),INTERVAL 1 DAY) from login group by user_id);

SQL68：牛客每个人最近的登录日期(四)

select login.date,ifnull(n1.new_num,0)
from login 
left join (
    select l1.date,count(distinct l1.user_id) new_num
    from login l1
    where l1.date = (
        select min(date) 
        from login 
        where user_id=l1.user_id
    )
    group by l1.date
) n1
on login.date = n1.date
group by login.date 
order by login.date