如果表查询中所有的列都包括在了索引中，就有可能使用FFS，当然也可以使用hint来选择FFS。下面看看使用不同方式访问索引的例子：
SQL> create index idx_un_tset_ownid_dataid on un_test (owner,data_object_id);
Index created.
Elapsed: 00:00:00.96
SQL> select owner ,data_object_id from un_test
2 where data_object_id >5;
6891 rows selected.
Elapsed: 00:00:00.06
Execution Plan
----------------------------------------------------------
Plan hash value: 287826149
-------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 6913 | 55304 | 32 (4)| 00:00:01 |
|* 1 | INDEX FAST FULL SCAN| IDX_UN_TSET_OWNID_DATAID | 6913 | 55304 | 32 (4)| 00:00:01 |
------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("DATA_OBJECT_ID">5)
Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
602 consistent gets
135 physical reads
0 redo size
..........
0 sorts (memory)
0 sorts (disk)
6891 rows processed
SQL> select owner ,data_object_id from un_test
2 where data_object_id =5;
no rows selected
Elapsed: 00:00:00.00
Execution Plan
----------------------------------------------------------
Plan hash value: 1786681723
---------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 8 | 21 (0)| 00:00:01 |
|* 1 | INDEX SKIP SCAN | IDX_UN_TSET_OWNID_DATAID | 1 | 8 | 21 (0)| 00:00:01 |
---------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("DATA_OBJECT_ID"=5)
filter("DATA_OBJECT_ID"=5)
Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
15 consistent gets
0 physical reads
。。。。。。
0 sorts (memory)
0 sorts (disk)
0 rows processed
SQL> select object_id from un_test where object_id = 5;
Elapsed: 00:00:00.01
Execution Plan
----------------------------------------------------------
Plan hash value: 333614268
--------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 5 | 1 (0)| 00:00:01 |
|* 1 | INDEX UNIQUE SCAN| I_TEST_UNI | 1 | 5 | 1 (0)| 00:00:01 |
--------------------------------------------------------------------------------
Predicate Information (identified by operation id):
-------------------------------------------------
1 - access("OBJECT_ID"=5)
Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
2 consistent gets
0 physical reads
。。。。。
0 sorts (disk)
1 rows processed
SQL> select /*+ index_ffs(a)*/ owner,data_object_id from un_test a
2 where wner = 'SYS';
23021 rows selected.
Elapsed: 00:00:00.12
Execution Plan
----------------------------------------------------------
Plan hash value: 287826149
-------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2668 | 21344 | 32 (4)| 00:00:01 |
|* 1 | INDEX FAST FULL SCAN| IDX_UN_TSET_OWNID_DATAID | 2668 | 21344 | 32 (4)| 00:00:01 |
-------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("OWNER"='SYS')
Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
1674 consistent gets
0 physical reads
。。。。。。。
0 sorts (memory)
0 sorts (disk)
23021 rows processed
----------------
SQL> SELECT /* INDEX(A)*/ OWNER,DATA_OBJECT_ID FROM UN_TEST A
2 WHERE WNER ='SYS';
23021 rows selected.
Elapsed: 00:00:00.12
Execution Plan
----------------------------------------------------------
Plan hash value: 3998526102
---------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2668 | 21344 | 8 (0)| 00:00:01 |
|* 1 | INDEX RANGE SCAN| IDX_UN_TSET_OWNID_DATAID | 2668 | 21344 | 8 (0)| 00:00:01 |
---------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("OWNER"='SYS')
Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
1586 consistent gets
0 physical reads
。。。。。
0 sorts (disk)
23021 rows processed
----------------------------
SQL> select /*+ index (a idx_un_test_ownid_dataid)*/ count(*) from un_test a
2 where data_object_id = 5;
Elapsed: 00:00:00.01
Execution Plan
----------------------------------------------------------
Plan hash value: 1636324484
---------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 2 | 21 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 2 | | |
|* 2 | INDEX SKIP SCAN| IDX_UN_TSET_OWNID_DATAID | 1 | 2 | 21 (0)| 00:00:01 |
---------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("DATA_OBJECT_ID"=5)
filter("DATA_OBJECT_ID"=5)
Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
15 consistent gets
0 physical reads
。。。。。
0 sorts (disk)
1 rows processed
---位图索引。。
SQL> select /*+ index(a idx_type_bit)*/ * from un_test a
2 where a.object_type ='TABLE';
2921 rows selected.
Elapsed: 00:00:00.05
Execution Plan
----------------------------------------------------------
Plan hash value: 4191918535
---------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1779 | 161K| 194 (0)| 00:00:03 |
| 1 | TABLE ACCESS BY INDEX ROWID | UN_TEST | 1779 | 161K| 194 (0)| 00:00:03 |
| 2 | BITMAP CONVERSION TO ROWIDS| | | | | |
|* 3 | BITMAP INDEX SINGLE VALUE | IDX_TYPE_BIT | | | | |
---------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("A"."OBJECT_TYPE"='TABLE')
Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
347 consistent gets
1 physical reads
0 sorts (memory)
0 sorts (disk)
2921 rows processed