declare
  cursor custs is
    select ROUND(SUM(item_qty)/count(distinct tran_id), 3) as avg, consumer_id
    from tranit_tran_item group by consumer_id;
 
begin
  for cust in custs 
    loop 
      update customers set avgtransvol = cust.avg where consumer_id = cust.consumer_id;
    end loop;
end;