In Adobe Flex, a most discussed limitation is that the Datagrid or AdvancedDataGrid components do not support a footer row for showing some aggregate functions.

A popular and simple solution for this is to create a secondary datagrid whose dataProvider is a aggregate collection of the master datagrid data.

But we need to handle certain properties for footer datagrid to achieve this. some of them are :

1) on stretch of the master datagrid columns, we need to change the column width of the footer datagrid also.

eg: we can write a columnStretchHandler and assign this method to the "columnStretch" property of the master datagrid as follows:

private function columnStretchHandler(event:AdvancedDataGridEvent):void {

  var dg:AdvancedDataGrid = event.target as AdvancedDataGrid;

  <footer_datagrid_id>.columns[event.columnIndex].width = 
   
        dg.columns[event.columnIndex].width; 

}

2) Other properties that may have to be set are :
rowCount="1"
showHeaders="false"
maxHeight="30"
sortExpertMode="true"
sortableColumns="false"