Bug 177504 Engine doesn't provide SubQuery for extended item
Engine doesn't provide SubQuery for extended item, so chart can't use container's binding to execute the query. If possible, engine could provide an option for extended item to choose whether engine could create the query, so extended item won't create SubQuery by itself.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/data/dte/ReportQueryBuilder.java
/**
		 * create all sort conditions given a sort key handle iterator
		 * 
		 * @param iter
		 *            the iterator
		 * @return sort array
		 */
		private ArrayList createSorts( Iterator iter )
		{
			ArrayList sorts = new ArrayList( );
			if ( iter != null )
			{
				while ( iter.hasNext( ) )
				{
					SortKeyHandle handle = (SortKeyHandle) iter.next( );
					sorts.add( createSort( handle ) );
				}
			}
			return sorts;
		}
		/**
		 * create all sort conditions in a listing element
		 * 
		 * @param listing
		 *            ListingDesign
		 * @return the sort array
		 */
		protected ArrayList createSorts( ListingDesign listing )
		{
			return createSorts( ( (ListingHandle) listing.getHandle( ) )