思路：以login为主表连接，找出每个用户的日期排名，从表中筛选rk=1的
select
u_n
,c_n
,date
from
(
select
u.name u_n
,c.name c_n
,date
,row_number()over(partition by u.name order by date desc) rk
from login l
left join user u on l.user_id = u.id
left join client c on l.client_id = c.id
) a
where rk = 1
order by u_n