Oracle SQL Plan operation BITMAP AND/OR

create table tq84_tab (
   val     number,
   flg_1   char(1) not null check (flg_1 in ('y', 'n')),
   flg_2   char(1) not null check (flg_2 in ('y', 'n')),
   dat     varchar2(20)
);

begin
   dbms_random.seed(42);
end;
/

insert into tq84_tab
select
   round(dbms_random.value(1,1000), 1),
   case when dbms_random.value > 0.975 then 'y' else 'n' end,
   case when dbms_random.value > 0.975 then 'y' else 'n' end,
   rpad('x', 20, 'x')
from
   dual
connect by level <= 10000;

create bitmap index tq84_tab_ix_1 on tq84_tab (flg_1);
create bitmap index tq84_tab_ix_2 on tq84_tab (flg_2);

explain plan for
select
   val
from
   tq84_tab
where
   flg_1 = 'y'   and
   flg_2 = 'y'
;

select * from table(dbms_xplan.display(format=>'basic'));
--
-- -------------------------------------------------------------
-- | Id  | Operation                           | Name          |
-- -------------------------------------------------------------
-- |   0 | SELECT STATEMENT                    |               |
-- |   1 |  TABLE ACCESS BY INDEX ROWID BATCHED| TQ84_TAB      |
-- |   2 |   BITMAP CONVERSION TO ROWIDS       |               |
-- |   3 |    BITMAP AND                       |               |
-- |   4 |     BITMAP INDEX SINGLE VALUE       | TQ84_TAB_IX_1 |
-- |   5 |     BITMAP INDEX SINGLE VALUE       | TQ84_TAB_IX_2 |
-- -------------------------------------------------------------


explain plan for
select
   val
from
   tq84_tab
where
   flg_1 = 'y'   or
   flg_2 = 'y'
;

select * from table(dbms_xplan.display(format=>'basic'));
--
-- -------------------------------------------------------------
-- | Id  | Operation                           | Name          |
-- -------------------------------------------------------------
-- |   0 | SELECT STATEMENT                    |               |
-- |   1 |  TABLE ACCESS BY INDEX ROWID BATCHED| TQ84_TAB      |
-- |   2 |   BITMAP CONVERSION TO ROWIDS       |               |
-- |   3 |    BITMAP OR                        |               |
-- |   4 |     BITMAP INDEX SINGLE VALUE       | TQ84_TAB_IX_1 |
-- |   5 |     BITMAP INDEX SINGLE VALUE       | TQ84_TAB_IX_2 |
-- -------------------------------------------------------------

drop   table tq84_tab;