oracle 只取字符串中的数字

create or replace  function getnumber(str varchar2) return varchar2  is
  rstr varchar2(4000);
begin
 
  if str is null then
      return null;
  else
      rstr := '';
      for i IN 1 .. length(str) loop
        if (ascii(substr(str, i, 1)) between 48 and 57) or
           (substr(str, i, 1) = '.') then
          rstr := rstr || substr(str, i, 1);
        end if;
      end loop;
      return rstr;
 end if;
end ;