Bug 122854 There is redundant columns in "available columns" list in "export data" dialog.
Description: There is redundant columns in "available columns" list in "export data" dialog. Steps to reproduce: 1. Preview attached design in web viewer. 2. Select the table and click on "export" button. 3. There is a "detail" column name in "available columns" list which is not data set column.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/impl/DataExtractionTask.java
*/
	private IExtractionResults extractByInstanceId( ) throws EngineException
	{
		assert instanceId != null;
		
		assert executionContext.getDataEngine() != null;
		DataEngine dataEngine = executionContext.getDataEngine().getDataEngine();
		
		ReportItemDesign rptItem = (ReportItemDesign) report
				.getReportItemByID( instanceId.getComponentID( ) );
		assert rptItem != null;
		
		IBaseQueryDefinition query = rptItem.getQuery();
		validateSelectedColumns( query );
		
		
		DataID dataId = instanceId.getDataID();
		InstanceID instId = instanceId;
		while( instId != null && dataId == null ){
			instId = instId.getParentID( );
			if( instId != null )
			{
				dataId = instId.getDataID();
			}
		}
		
		if(dataId == null)
			return null;
		
		DataSetID dataSetId = dataId.getDataSetID( );