AX query - sorting with sum field

select  sum(NETAMOUNT),CUSTACCOUNT
from RETAILTRANSACTIONTABLE
group by CUSTACCOUNT
order by sum(NETAMOUNT) desc

            qbds.addGroupByField(fieldNum(RetailTransactionTable, CustAccount));   
            qbds.addSelectionField(fieldNum(RetailTransactionTable,netAmount),SelectionField::Sum);  
            qbds.addSortField(fieldNum(RetailTransactionTable,netAmount),SortOrder::Descending);