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 totalExpressionBindings;
		}
		private void addNewColumnBindings( IBaseQueryDefinition query,
				ITotalExprBindings totalExpressionBindings )
		{
			IColumnBinding[] bindings = totalExpressionBindings.getColumnBindings( );
			if ( bindings != null )
			{
				for ( int i = 0; i < bindings.length; i++ )
				{
					addColumnBinding( query, bindings[i] );
				}
			}
		}
		private void addColumnBinding( IBaseQueryDefinition transfer,
				IColumnBinding binding )
		{
			assert transfer != null;
			transfer.getResultSetExpressions( )
					.put( binding.getResultSetColumnName( ),
							binding.getBoundExpression( ));
		}
		private IConditionalExpression createConditionalExpression( RuleDesign rule )
		{
			ConditionalExpression expression = new ConditionalExpression( rule
					.getTestExpression( ),
					toDteFilterOperator( rule.getOperator( ) ), rule.getValue1( ),
					rule.getValue2( ) );
			return ExpressionUtil.transformConditionalExpression( expression );
		}