oracle 只取字符串中的数字

oracle 只取字符串中的数字
  function getnumber(str varchar2) return varchar2 is --by yanleigis Email:landgis@126.com
    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;