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
{
			return createFilters( group.filtersIterator( ) );
		}
		/**
		 * create filter array given a ExtendedItemHandle
		 * 
		 * @param group
		 *            the GroupHandle
		 * @return filter array
		 */
		public ArrayList createFilters( ExtendedItemDesign extendedItem )
		{
			return createFilters( ( (ExtendedItemHandle) extendedItem
					.getHandle( ) ).filtersIterator( ) );
		}
		/**
		 * create one sort condition
		 * 
		 * @param handle
		 *            the SortKeyHandle
		 * @return the sort object
		 */
		private ISortDefinition createSort( SortKeyHandle handle )
		{
			SortDefinition sort = new SortDefinition( );
			sort.setExpression( handle.getKey( ) );
			sort.setSortDirection( handle.getDirection( ).equals(
					DesignChoiceConstants.SORT_DIRECTION_ASC ) ? 0 : 1 );
			return sort;
		}