SQLで日ごとに累計したい

select
  date_format(a.created_at, '%Y-%m-%d') as created_on,
  count(*) as count
from
  users a
group by
  created_on
order by
  created_on;

select
  date_format(a.created_at, '%Y-%m-%d') as created_on,
  (
    select
      count(*)
    from
      users
    where
      date_format(created_at, '%Y-%m-%d') <= date_format(a.created_at, '%Y-%m-%d')
  ) as count
from
  users a
group by
  created_on
order by
  created_on;

create database if not exists sample_database;
use sample_database;

drop table users;
create table users (
  id integer auto_increment not null,
  name varchar(256) not null,
  created_at datetime not null,
  primary key (id)
);

insert into users (name, created_at) values 
('user1', '2014-10-20 18:17:53'),
('user2', '2014-10-20 18:17:57'),
('user3', '2014-10-21 18:18:03'),
('user4', '2014-10-22 18:18:14'),
('user5', '2014-10-22 18:18:18');

select
  date_format(a.created_at, '%Y-%m-%d') as created_on,
  count(*) as count
from
  users a
group by
  created_on
order by
  created_on;

select
  date_format(a.created_at, '%Y-%m-%d') as created_on,
  ANY_VALUE(
    (
      select
        count(*)
      from
        users
      where
        date_format(created_at, '%Y-%m-%d') <= date_format(a.created_at, '%Y-%m-%d')
    )
  ) as count
from
  users a
group by
  created_on
order by
  created_on;