declare
  avg NUMBER(8, 3);
  cursor custs is 
    select MONTHS_BETWEEN(MAX(purch_date), MIN(purch_date)) as totalmonth, consumer_id 
    from tranit_tran_item group by consumer_id;

begin 
  for cust in custs 
    loop 
       select ROUND(SUM(prc_paid_amt)/cust.totalmonth), 3) into avg from tranit_tran_item where consumer_id = cust.consumer_id;
       update customers set avgspend = avg where consumer_id = cust.consumer_id; 
    end loop;
end;