--向某个分区插入数据
 insert into t select 9, '9' 
from dual connect by rownum<1e4 ;
commit;

 exec dbms_stats.set_table_prefs(user,'T','PUBLISH','FALSE');

--统计信息没变
exec dbms_stats.gather_table_stats(user,'T');
 select num_rows,blocks,last_analyzed
    from user_tab_statistics
     where table_name ='T';
 NUM_ROWS     BLOCKS LAST_ANAL
---------- ---------- ---------
         5        230 27-SEP-16
         1         46 27-SEP-16
         1         46 27-SEP-16
         1         46 27-SEP-16
         1         46 27-SEP-16
         1         46 27-SEP-16

--Pending statistics
select num_rows,blocks
    from user_tab_pending_stats
    where table_name ='T';
  NUM_ROWS     BLOCKS
---------- ----------
     10000         46
         1         46
         1         46
         1         46
         1         46
     10004        230

--使用Pending statistics
 alter session set optimizer_use_pending_statistics=true;
select count(*) from t where id = 9;


 select * from table(dbms_xplan.display_cursor);
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID  g1usps76kb8yz, child number 0
-------------------------------------
select count(*) from t where id = 9


Plan hash value: 2993254470


------------------------------------------------------------------------------------------------
| Id  | Operation               | Name | Rows  | Bytes | Cost (%CPU)| Time     | Pstart| Pstop |
------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT        |      |       |       |    10 (100)|          |       |       |
|   1 |  SORT AGGREGATE         |      |     1 |     3 |            |          |       |       |
|   2 |   PARTITION RANGE SINGLE|      |     1 |     3 |    10   (0)| 00:00:01 |     1 |     1 |
|*  3 |    TABLE ACCESS FULL    | T    |     1 |     3 |    10   (0)| 00:00:01 |     1 |     1 |
------------------------------------------------------------------------------------------------


Predicate Information (identified by operation id):
---------------------------------------------------


   3 - filter("ID"=9)






select count(*) from t;
 select * from table(dbms_xplan.display_cursor);
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID  cyzznbykb509s, child number 1
-------------------------------------
select count(*) from t


Plan hash value: 3225603066


-------------------------------------------------------------------------------------
| Id  | Operation            | Name | Rows  | Cost (%CPU)| Time     | Pstart| Pstop |
-------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT     |      |       |    43 (100)|          |       |       |
|   1 |  SORT AGGREGATE      |      |     1 |            |          |       |       |
|   2 |   PARTITION RANGE ALL|      |     5 |    43   (0)| 00:00:01 |     1 |     5 |
|   3 |    TABLE ACCESS FULL | T    |     5 |    43   (0)| 00:00:01 |     1 |     5 |
-------------------------------------------------------------------------------------

rows没变, 
需要invalid现存的cursor, Pending statistics才能生效