Remove all alphabetic characters from a string

select to_number(replace(translate(upper(column_name),'ABCDEFGHIJKLMNOPQRSTUVWXYZ','X'),'X')) FOO from table_name order by FOO;

Example:

select to_number(replace(translate(upper('123xj456iu789'),'ABCDEFGHIJKLMNOPQRSTUVWXYZ','X'),'X')) FOO from dual

FOO   
------
123456789
1 rows selected