Function for record log old value -> new value

CREATE OR REPLACE function check_value(v_col in varchar2,
                                       v_old in varchar2,
                                       v_new in varchar2) return varchar2 is
  Result varchar2(2000);
begin
  if v_old is null and v_new is null then
    result := '';
  elsif v_old is null and v_new is not null then
    result := v_col || '=' || v_new || '; ';
  elsif v_old is not null and v_new is null then
    result := v_col || '=' || v_old || '->DELETED; ';
  else
    if v_old = v_new then
      result := '';
    else
      result := v_col || '=' || v_old || '->' || v_new || '; ';
    end if;
  end if;
  return(Result);
end;
/