从这个公式可以推断走索引范围扫描的成本可以近似看作是和聚簇因子成正比，因此，聚簇因子值的大小实际上对CBO判断是否走相关的索引起着至关重要的作用。
演示一个例子，通过修改聚簇索引的值就让原本走索引范围扫描的执行计划变成了走全表扫描：
linuxidc@MYDB>create table t1 as select * from dba_objects;
Table created.
linuxidc@MYDB>create index idx_t1 on t1(object_id);
Index created.
linuxidc@MYDB>select clustering_factor from dba_indexes where index_name='IDX_T1';
CLUSTERING_FACTOR
-----------------
1063
linuxidc@MYDB>select /*+ cluster_factor_expmple_1 */ object_id,object_name from t1 where object_id between 103 and 108;
OBJECT_ID OBJECT_NAME
---------- ------------------------------
103 MIGRATE$
104 DEPENDENCY$
105 ACCESS$
106 I_DEPENDENCY1
107 I_DEPENDENCY2
108 I_ACCESS1
6 rows selected.
linuxidc@MYDB>select * from table(dbms_xplan.display_cursor(null,null,'all'));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID ga3jv3kwwwmx5, child number 0
-------------------------------------
select /*+ cluster_factor_expmple_1 */ object_id,object_name from t1
where object_id between 103 and 108
Plan hash value: 50753647
--------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 3 (100)| |
| 1 | TABLE ACCESS BY INDEX ROWID| T1 | 6 | 474 | 3 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | IDX_T1 | 6 | | 2 (0)| 00:00:01 |
--------------------------------------------------------------------------------------
......省略部分输出
SQL走了索引范围扫描，成本值为3
使用Hint强制SQL走全表扫描：
linuxidc@MYDB>select /*+ full(t1) */ object_id,object_name from t1 where object_id between 103 and 108;
OBJECT_ID OBJECT_NAME
---------- ------------------------------
103 MIGRATE$
104 DEPENDENCY$
105 ACCESS$
106 I_DEPENDENCY1
107 I_DEPENDENCY2
108 I_ACCESS1
6 rows selected.
linuxidc@MYDB>select * from table(dbms_xplan.display_cursor(null,null,'all'));
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID b7hjwuvmg2ncy, child number 0
-------------------------------------
select /*+ full(t1) */ object_id,object_name from t1 where object_id
between 103 and 108
Plan hash value: 3617692013
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 287 (100)| |
|* 1 | TABLE ACCESS FULL| T1 | 6 | 474 | 287 (1)| 00:00:04 |
--------------------------------------------------------------------------
......省略部分输出
现在SQL走全表扫描，成本值为287。