SQL> select count(1) from bin_idx_tab;

  COUNT(1)
----------
      9001

SQL> select unique * from bin_idx_tab;

         A B
---------- --
         1 A
         1 B
         1 C
         2 A
         2 B
         2 C
         3 A
         3 B
         3 C

9 rows selected.

SQL> create bitmap index btm01 on bin_idx_tab(a,b);

Index created.

SQL> exec dbms_stats.gather_table_stats(ownname=>user, tabname=>'bin_idx_tab', cascade=>true);

PL/SQL procedure successfully completed.

SQL> set autotrace traceonly
SQL> select * from bin_idx_tab where (a=1 and b='C') or (a=2 and b='B');

2000 rows selected.


Execution Plan
----------------------------------------------------------
   0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=1 Card=2000 Bytes=
          10000)

   1    0   BITMAP CONVERSION (TO ROWIDS) (Cost=1 Card=2000 Bytes=1000
          0)

   2    1     BITMAP INDEX (FAST FULL SCAN) OF 'BTM01' (INDEX (BITMAP)
          )

Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
          5  consistent gets
          0  physical reads
          0  redo size
      26852  bytes sent via SQL*Net to client
       1971  bytes received via SQL*Net from client
        135  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
       2000  rows processed

SQL> drop index btm01;

Index dropped.

SQL> select * from bin_idx_tab where (a=1 and b='C') or (a=2 and b='B');

2000 rows selected.


Execution Plan
----------------------------------------------------------
   0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=6 Card=2000 Bytes=
          10000)

   1    0   TABLE ACCESS (FULL) OF 'BIN_IDX_TAB' (TABLE) (Cost=6 Card=
          2000 Bytes=10000)

Statistics
----------------------------------------------------------
        158  recursive calls
          0  db block gets
        174  consistent gets
          0  physical reads
          0  redo size
      26852  bytes sent via SQL*Net to client
       1971  bytes received via SQL*Net from client
        135  SQL*Net roundtrips to/from client
          3  sorts (memory)
          0  sorts (disk)
       2000  rows processed