create table commands

what's the different about the following cmds?

1.

create table aaa ( a1 int )

on 'seg_test'

partition by roundrobin 1 on ( 'seg_test')

2.

create table bbb ( a1 int )

on 'default'

3.

create table ccc ( a1 int )

on 'default'

partition by roundrobin 1 on ('seg_test')

the 1st and 2nd is clear, but what happne if I create table using 3rd cmd?