private void checkAggregation()
	{
		if(group!=null)
		{
			ExpressionDecomposer ed=new ExpressionDecomposer();
			Iterator<Expression> s=select.iterator();
			while(s.hasNext())
			{
				Expression e=s.next();

				if(!e.getType().equals("sum") && !e.getType().equals("avg"))
				{
					ArrayList<String> selectAttrs=ed.getIdentifiers(e);
					Iterator<String> selectIterator=selectAttrs.iterator();

					while(selectIterator.hasNext())
					{		
						String next=selectIterator.next();
						if(!next.equals(group))
						{
							System.out.println("Error: Selected attributes not in grouping " +
									"attributes! \n\t ("+next+") is not in grouping attributes!");
						}
					}
				}
			}
		}
	}