You can make Oracle change the character sort order using the NLSSORT function, eg:
select * from (
select 'ab' x from dual
union select 'Az' from dual
union select 'Bz' from dual
union select 'äm' from dual
union select 'ba' from dual ) x
order by nlssort(x, 'NLS_SORT=LATIN')
will give the results:
ab
äm
Az
ba
Bz
You can obtain a list of valid sort orders by running the query:
select * from v$nls_valid_values where parameter='SORT' order by 1, 2
