select sum((VALUE_OF_BAL_QTY_DATED(sum(qty), sale_type, sale_code, to_date('31012012', 'ddmmyyyy')  ) ))
  from
(Select sale_type, sale_code, qty
    from invp
    where invdate <=to_date('31012012', 'ddmmyyyy')
union all
Select sale_type, sale_code, qty*-1
    from invs
    where invdate <=to_date('31012012', 'ddmmyyyy') )
group by sale_type, sale_code

CREATE OR REPLACE FUNCTION VALUE_OF_BAL_QTY_DATED
  (pin_balqty        IN NUMBER,
   pin_sale_type       IN CHAR, 
   pin_sale_code	IN char,
   pin_dated	     IN DATE) RETURN number IS
.......
.......

CREATE OR REPLACE FUNCTION VALUE_OF_BAL_QTY_DATED
  (pin_balqty        IN NUMBER,
   pin_sale_type       IN CHAR, 
   pin_sale_code	IN char,
   pin_dated	     IN DATE) RETURN number IS
   a NUMBER := 0;
   b NUMBER := pin_balqty;
  BEGIN
     b := pin_balqty;
     FOR j in (	Select *  
		FROM V0PROD
		where	sale_type=pin_sale_type and sale_code=pin_sale_code  
		and 	(invdate <=pin_dated or invdate is null)
		ORDER BY sale_type, sale_code,   decode(invdate, null, 0, 1) desc , INVDATE DESC, INVNO DESC ) LOOP
             IF b <= j.qty THEN
               a:= (b * j.uprice)+a;
               RETURN a;
             ELSE
               a:= (j.qty * j.uprice)+a;
               b:= b-j.qty;
             END IF;
     END LOOP;
     RETURN a;
  END;
/

  select sum(VALUE_OF_BAL_QTY_DATED(sum(qty), sale_type, sale_code, medate))
  into einv
  from
 (Select sale_type, sale_code, nvl(qty,0) qty
     from invp
     where invdate <=medate
 union all
 Select sale_type, sale_code, nvl(qty,0)*-1
     from invs
     where invdate <=medate)
 group by sale_type, sale_code;