ㅋ.ㅋ... 이렇게 하니깐 되네요.. ^^

create or replace
PROCEDURE TEST_SP ( v_out_cursor OUT SYS_REFCURSOR )
IS
BEGIN
    OPEN v_out_cursor FOR
    WITH t AS
    (SELECT '20100610' yyyymmdd, 'ABC' gubun1, 'K2' gubun2, 2288 qty1, 3850 qty2 FROM DUAL
     UNION ALL
     SELECT '20100611' yyyymmdd, 'ABC' gubun1, 'K2' gubun2, 6336 qty1, 2200 qty2 FROM DUAL
     UNION ALL
     SELECT '20100612' yyyymmdd, 'ABC' gubun1, 'K2' gubun2, 3190 qty1, 2750 qty2 FROM DUAL
     UNION ALL
     SELECT '20100613' yyyymmdd, 'ABC' gubun1, 'K2' gubun2, 7722 qty1, 4312 qty2 FROM DUAL)
   SELECT yyyymmdd, gubun1, gubun2, qty1, qty2, NVL (temp_qty1 - temp_qty2, 0) new_field
      FROM (SELECT yyyymmdd, gubun1, gubun2, qty1, qty2,
                                   LAG (qty1) OVER (ORDER BY yyyymmdd) temp_qty1,
                                   LAG (qty2) OVER (ORDER BY yyyymmdd) temp_qty2
                       FROM t)
;
END TEST_SP;