Query and calculated fields

How can I add a calculated field to a query at runtime?

For a TTable I use:

  Table1.Close;

  for i := 0 to Table1.FieldDefs.Count - 1 do
    if Table1.FindField( Table1.FieldDefs[ i ].Name ) = nil then
      Table1.FieldDefs.Items[ i ].CreateField( Table1 );

  f := TStringField.Create( Table1 );
  f.Name := 'FULLNAME';
  f.FieldName := 'FULLNAME';
  f.Size := 50;
  f.Calculated := True;
  f.DataSet := Table1;

  Table1.OnCalcFields := Form1.Table1CalcFields;

  Table1.Open;
...
procedure TForm1.Table1CalcFields(DataSet: TDataSet);
begin
   Table1.FieldByName('FULLNAME').AsString := Table1.FieldByName('FIRSTNAME').AsString + ' ' + Table1.FieldByName('LASTNAME').AsString;
end;

For this work perfect but for Query not. Any HEEEEELLLLPPPP ??