Oracle SQL Plan operation SORT GROUP BY NOSORT

create table tq84_tab (
    g   char    (1) not null,
    v   number  (2) not null,
    x   varchar2(3) not null
);

begin
   insert into tq84_tab values ('A',   1, 'z');
   insert into tq84_tab values ('A',   2, 'y');
   insert into tq84_tab values ('A',   3, 'x');
   insert into tq84_tab values ('B',   4, 'w');
   insert into tq84_tab values ('C',   5, 'v');
   insert into tq84_tab values ('C',   6, 'u');
end;
/

create index tq84_ix on tq84_tab (g, v);

explain plan for
select
   g,
   any_value(v)
from
   tq84_tab
group by
   g;

select * from dbms_xplan.display(format => 'basic');
--
-- ----------------------------------------
-- | Id  | Operation            | Name    |
-- ----------------------------------------
-- |   0 | SELECT STATEMENT     |         |
-- |   1 |  SORT GROUP BY NOSORT|         |
-- |   2 |   INDEX FULL SCAN    | TQ84_IX |
-- ----------------------------------------

drop table tq84_tab;