ADCommand1.CommandText.Text := 'select * from MyTab {if !cond} where !cond {fi}';
ADCommand1.Macros[0].AsString := 'ID > 100';
ADCommand1.Prepare;
ShowMessage(ADCommand1.SQLText); // select * from MyTab where ID > 100
ADCommand1.Macros[0].Clear;
ADCommand1.Prepare;
ShowMessage(ADCommand1.SQLText); // select * from MyTab