public int addAggregate(AggregateFunctionExpression aggregate){
  int position=groupBy.size() + aggregates.size();
  aggregates.add(aggregate);
  options.add(aggregate.getOption());
  return position;
}

public int addAggregate ( AggregateFunctionExpression aggregate ) { int position = groupBy . size ( ) + aggregates . size ( ) ; aggregates . add ( aggregate ) ; options . add ( aggregate . getOption ( ) ) ; return position ; }
add a new aggregate and return its position .
