Bug 124251 the data cann't been exported.
Description: the data cann't been exported. Steps to reproduce: 1. new a report 2. new a datasource and a data set(DS_A) 3. use an external library 4. drag a table to the report layout from the imported library 5. insert an another table into the layout of the report and bind the data set(DS_A) 6. preview in the 'Web Viewer' and export the data Actual result: The data can been exported. Expect result: The data can been exporteded
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/impl/DataExtractionTask.java
/*
	 * check if the selected columns is valid, if no column is selected, then initialize the
	 * selected column using row expression.
	 */
	private void validateSelectedColumns( IBaseQueryDefinition query )
			throws EngineException
	{
		assert query != null;
		
		Collection exprs = getValueExpressions( query );
		if ( selectedColumns != null )
		{
			for ( int i = 0; i < selectedColumns.length; i++ )
			{
				boolean findColumn = false;
				String selectColumn = selectedColumns[i].replaceAll( "\\s", "" );
				Iterator iter = exprs.iterator( );
				while ( iter.hasNext( ) )
				{
					IScriptExpression expr = (IScriptExpression) iter.next( );
					String exprText = expr.getText( ).replaceAll( "\\s", "" );
					if( exprText.equalsIgnoreCase( selectColumn ))
					{
						findColumn = true;
						break;
					}
				}
				if ( findColumn == false )
				{