Oracle SQL Plan operation: WINDOW (SORT PUSHED RANK)

create table tq84_tab (
   num number,
   dat date,
   val varchar2(100)
);

-- With the following index, the plan
-- operation WINDOW NOSORT STOPKEY would
-- be used.
--
-- create index tab_ix on tq84_tab(num, dat);

explain plan for
select
   dat,
   val
from
   tq84_tab
where
   num = 42 
order by
   dat desc
fetch first 2 row only;

select * from table(dbms_xplan.display(format=>'basic'));
--
-- ---------------------------------------------
-- | Id  | Operation                | Name     |
-- ---------------------------------------------
-- |   0 | SELECT STATEMENT         |          |
-- |   1 |  VIEW                    |          |
-- |   2 |   WINDOW SORT PUSHED RANK|          |
-- |   3 |    TABLE ACCESS FULL     | TQ84_TAB |
-- ---------------------------------------------

drop   table tq84_tab;