从执行计划中可以看出，成本已经由3变为105(即增加了102)，这说明我们对索引IDX_T1的聚簇因子的调整生效了。

要使成本值大于287，只需要把聚簇因子的值调整到400万。

linuxidc@MYDB>exec dbms_stats.set_index_stats(ownname=>'ZX',indname=>'IDX_T1',clstfct=>4000000,no_invalidate=>false);
?
PL/SQL procedure successfully completed.
?
linuxidc@MYDB>select clustering_factor from dba_indexes where index_name='IDX_T1';
?
CLUSTERING_FACTOR
-----------------
? ? ? ? ? 4000000
?
linuxidc@MYDB>select /*+ cluster_factor_expmple_3 */ 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? cwkc8q61bypa6, child number 0
-------------------------------------
select /*+ cluster_factor_expmple_3 */ 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 |
--------------------------------------------------------------------------

从上面显示的内容可以看出执行计划从索引范围扫描变成了全表扫描。