no_swap_join_inputs 与 leading

http://blog.csdn.net/jgmydsai/article/details/18221751?ADUIN=604178834&ADSESSION=1389577130&ADTAG=CLIENT.QQ.5275_.0&ADPUBNO=26274

首先建立测试用表如下

 create table t1 as select * from dba_objects;
 create table t2 as select * from dba_objects;
 create table t3 as select * from dba_objects;
 create table t4 as select * from dba_objects;

如下语句用leading改驱动表无效

 SELECT /*+ leading(t1) use_hash(t1 t2)  use_hash(t1 t3) */
  t1.object_id,t2.object_name,t3.object_name
   FROM t1
  INNER JOIN t2 ON (t1.object_id = t2.object_id)
  INNER JOIN t3 ON (t1.object_name = t3.object_name)

 Execution Plan
 ----------------------------------------------------------
 Plan hash value: 1573120526

 ------------------------------------------------------------------------------------
 | Id  | Operation       | Name | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
 ------------------------------------------------------------------------------------
 |   0 | SELECT STATEMENT    |      |  1218K|   260M|       |  2841   (1)| 00:00:35 |
 |*  1 |  HASH JOIN      |      |  1218K|   260M|  8656K|  2841   (1)| 00:00:35 |
 |   2 |   TABLE ACCESS FULL | T3   |   113K|  7320K|       |   347   (1)| 00:00:05 |
 |*  3 |   HASH JOIN     |      | 77853 |    11M|  8576K|  1445   (1)| 00:00:18 |
 |   4 |    TABLE ACCESS FULL| T1   | 96439 |  7440K|       |   347   (1)| 00:00:05 |
 |   5 |    TABLE ACCESS FULL| T2   | 77853 |  6006K|       |   347   (1)| 00:00:05 |
 ------------------------------------------------------------------------------------

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

    1 - access("T1"."OBJECT_NAME"="T3"."OBJECT_NAME")
    3 - access("T1"."OBJECT_ID"="T2"."OBJECT_ID")

 Note
 -----
    - dynamic sampling used for this statement (level=2)

这时可以与no_swap_join_inputs配合

 SELECT /*+ no_swap_join_inputs(t3) leading(t1) use_hash(t1 t2)  use_hash(t1 t3) */
  t1.object_id,t2.object_name,t3.object_name
   FROM t1
  INNER JOIN t2 ON (t1.object_id = t2.object_id)
  INNER JOIN t3 ON (t1.object_name = t3.object_name);
 Execution Plan
 ----------------------------------------------------------
 Plan hash value: 261998084

 ------------------------------------------------------------------------------------
 | Id  | Operation       | Name | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
 ------------------------------------------------------------------------------------
 |   0 | SELECT STATEMENT    |      |  1218K|   260M|       |  2841   (1)| 00:00:35 |
 |*  1 |  HASH JOIN      |      |  1218K|   260M|    12M|  2841   (1)| 00:00:35 |
 |*  2 |   HASH JOIN     |      | 77853 |    11M|  8576K|  1445   (1)| 00:00:18 |
 |   3 |    TABLE ACCESS FULL| T1   | 96439 |  7440K|       |   347   (1)| 00:00:05 |
 |   4 |    TABLE ACCESS FULL| T2   | 77853 |  6006K|       |   347   (1)| 00:00:05 |
 |   5 |   TABLE ACCESS FULL | T3   |   113K|  7320K|       |   347   (1)| 00:00:05 |
 ------------------------------------------------------------------------------------

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

    1 - access("T1"."OBJECT_NAME"="T3"."OBJECT_NAME")
    2 - access("T1"."OBJECT_ID"="T2"."OBJECT_ID")

 Note
 -----
    - dynamic sampling used for this statement (level=2)

 SELECT /*+ no_swap_join_inputs(t3) leading(t2) use_hash(t1 t2)  use_hash(t1 t3) */
  t1.object_id,t2.object_name,t3.object_name
   FROM t1
  INNER JOIN t2 ON (t1.object_id = t2.object_id)
  INNER JOIN t3 ON (t1.object_name = t3.object_name);
 Execution Plan
 ----------------------------------------------------------
 Plan hash value: 1184213596

 ------------------------------------------------------------------------------------
 | Id  | Operation       | Name | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
 ------------------------------------------------------------------------------------
 |   0 | SELECT STATEMENT    |      |  1218K|   260M|       |  2841   (1)| 00:00:35 |
 |*  1 |  HASH JOIN      |      |  1218K|   260M|    12M|  2841   (1)| 00:00:35 |
 |*  2 |   HASH JOIN     |      | 77853 |    11M|  6920K|  1445   (1)| 00:00:18 |
 |   3 |    TABLE ACCESS FULL| T2   | 77853 |  6006K|       |   347   (1)| 00:00:05 |
 |   4 |    TABLE ACCESS FULL| T1   | 96439 |  7440K|       |   347   (1)| 00:00:05 |
 |   5 |   TABLE ACCESS FULL | T3   |   113K|  7320K|       |   347   (1)| 00:00:05 |
 ------------------------------------------------------------------------------------

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

    1 - access("T1"."OBJECT_NAME"="T3"."OBJECT_NAME")
    2 - access("T1"."OBJECT_ID"="T2"."OBJECT_ID")

 Note
 -----
    - dynamic sampling used for this statement (level=2)