SQL> select /*+ index_combine(test ind_type ind_owner) */ * from test where object_type='TABLE' and wner='SCOTT';
Elapsed: 00:00:00.00

Execution Plan
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Plan hash value: 4279409151

----------------------------------------------------------------------------------------------
| Id  | Operation                        | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                 |           |     5 |   465 |    37   (3)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID     | TEST      |     5 |   465 |    37   (3)| 00:00:01 |
|   2 |   BITMAP CONVERSION TO ROWIDS    |           |       |       |            |          |
|   3 |    BITMAP AND                    |           |       |       |            |          |
|   4 |     BITMAP CONVERSION FROM ROWIDS|           |       |       |            |          |
|*  5 |      INDEX RANGE SCAN            | IND_OWNER |       |       |     3   (0)| 00:00:01 |
|   6 |     BITMAP CONVERSION FROM ROWIDS|           |       |       |            |          |
|*  7 |      INDEX RANGE SCAN            | IND_TYPE  |       |       |    32   (0)| 00:00:01 |
----------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
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   5 - access("OWNER"='SCOTT')
   7 - access("OBJECT_TYPE"='TABLE')

位图计划也可以用在B-TREE索引上。其思想是数据库引擎能够基于B-TREE索引扫描结果在内存中构建对应的位图。BITMAP CONVERSION FROM ROWIDS负责执行计划中的转换。