private void setJoined(String a, String b)
	{
		// insert both the a->b and the b->a combination, as this makes queries
		// faster.
		// a->b combo
		ArrayList<String> aList = joinedTables.get(a);
		if (aList == null)
		{
			aList = new ArrayList<String>();
			joinedTables.put(a, aList);
		}
		if (!aList.contains(b))
		{
			aList.add(b);
		}
		// b->a combo
		ArrayList<String> bList = joinedTables.get(b);
		if (bList == null)
		{
			bList = new ArrayList<String>();
			joinedTables.put(b, bList);
		}
		if (!bList.contains(a))
		{
			bList.add(a);
		}
	}