Solution for MySQL which doesn't have concepts of partition KEEP, DENSE_RANK. Works for other SQL DBs too.

select userid,
       my_date,
       ...
from
(
select @sno:= case when @pid<>userid then 0
                    else @sno+1
    end as serialnumber, 
    @pid:=userid,
       my_Date,
       ...
from   users order by userid, my_date
) a
where a.serialnumber=0

Reference: http://benincampus.blogspot.com/2013/08/select-rows-which-have-maxmin-value-in.html

Solution for MySQL which doesn't have concepts of partition KEEP, DENSE_RANK.

select userid,
       my_date,
       ...
from
(
select @sno:= case when @pid<>userid then 0
                    else @sno+1
    end as serialnumber, 
    @pid:=userid,
       my_Date,
       ...
from   users order by userid, my_date
) a
where a.serialnumber=0

Reference: http://benincampus.blogspot.com/2013/08/select-rows-which-have-maxmin-value-in.html