var
   IfIChangeThisTableDataWillBeLost : Boolean;
begin
   with DBISAMTable do
      begin
      FieldDefs.Add('Password', ftInteger, 0, True, '0');
      FieldDefs.Add('Name', ftString, 6, False);
      IfIChangeThisTableDataWillBeLost := True;
      if IfIChangeThisTableDataWillBeLost then
         FieldDefs.Add('ExtraField', ftInteger, 0, True, '5');
      AlterTable();
      end;
end;