At design time you can group nested tables only using the GroupedColumns collection editor since the drop-by area is not shown automatically.
At runtime you can make the drop-by area show up by adding the folling line in your forms ctor:
whereas "Orders" needs to be replaced with the name of the nested table.
Check out the HierarchySample and HierarchyView. They both show drop-by area for nested tables.
If you need to get access to the GroupedColumns collection of a nested relation at runtime, you can use the following call: