位图索引的一大优势便是可以对索引使用逻辑操作，如 and or等。Bitmap Minus Operation 是位图索引逻辑操作的一种，在类似 where c1 = :v1 and not c2 = :v2 的情况下，有可能会发生Bitmap Minus Operation。
SQL> create table t1(c1 number,c2 number,c3 varchar2(20));
表已创建。
SQL> create bitmap index i1 on t1(C1);
索引已创建。
SQL> create bitmap index i2 on t1(c2);
索引已创建。
SQL> insert into t1 select rownum,rownum,rownum from dual connect by level < 10000;
已创建9999行。
SQL> insert into t1 select * from t1;
已创建9999行。
SQL> commit;
通过hint强制优化器使用Bitmap Minux Operation
SQL> l
1* select /*+index_combine(t1 i1 i2 ) */ * from t1 where c1=1 and not c2 =2
SQL> /
C1 C2 C3
---------- ---------- --------------------
1 1 1
1 1 1
执行计划
----------------------------------------------------------
Plan hash value: 3546974129
--------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2 | 76 | 14 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID | T1 | 2 | 76 | 14 (0)| 00:00:01 |
| 2 | BITMAP CONVERSION TO ROWIDS | | | | | |
| 3 | BITMAP MINUS | | | | | |
| 4 | BITMAP MINUS | | | | | |
|* 5 | BITMAP INDEX SINGLE VALUE| I1 | | | | |
|* 6 | BITMAP INDEX SINGLE VALUE| I2 | | | | |
|* 7 | BITMAP INDEX SINGLE VALUE | I2 | | | | |
--------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
5 - access("C1"=1)
-- 6 - access("C2" IS NULL)
7 - access("C2"=2)
通过这里我们看到，总共执行了两次Bitmap Minus。这是因为除了排除c2=2的行，oracle还排除了C2 IS NULL的行（除非c2具有非空约束）。
SQL> alter table t1 modify c2 not null;
表已更改。
SQL> select /*+index_combine(t1 i1 i2 ) */ * from t1 where c1=1 and not c2 =2;
C1 C2 C3
---------- ---------- --------------------
1 1 1
1 1 1
执行计划
----------------------------------------------------------
Plan hash value: 3468972141
-------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2 | 76 | 13 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID | T1 | 2 | 76 | 13 (0)| 00:00:01 |
| 2 | BITMAP CONVERSION TO ROWIDS| | | | | |
| 3 | BITMAP MINUS | | | | | |
|* 4 | BITMAP INDEX SINGLE VALUE| I1 | | | | |
|* 5 | BITMAP INDEX SINGLE VALUE| I2 | | | | |
-------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
4 - access("C1"=1)
5 - access("