Pesquisa Com RadioGroup

procedure TfrSQL.RadioGroup1Click(Sender: TObject);
begin
  IBQuery1.Close;
  IBQuery1.Sql.Clear;
  IBQuery1.Sql.Add('Select * from Professor');
  IBQuery1.Sql.Add('inner join Titulo');
  IBQuery1.Sql.Add('on Professor.CdTitulo = Titulo.CdTitulo');
  case RadioGroup1.ItemIndex of
    0: IBQuery1.Sql.Add('order by DscTitulo, NomeProf');
    1: IBQuery1.Sql.Add('order by NomeProf');
    2: IBQuery1.Sql.Add('order by Sexo, NomeProf');
    3: IBQuery1.Sql.Add('order by Idade desc');
  end;
  IBQuery1.Open;
end;