hash join外连接可以指定驱动表

hash join 外连接改变驱动表:


 select  /*+ swap_join_inputs(e) use_hash(e,d)*/ e.ename,e.job,d.dname from emp e left join dept d  on e.deptno=d.deptno 

SQL> explain plan for select  /*+ swap_join_inputs(e) use_hash(e,d)*/ e.ename,e.job,d.dname from emp e left join dept d  on e.deptno=d.deptno ;

已解释。

SQL> select * from table(dbms_xplan.display());

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 3387915970

---------------------------------------------------------------------------
| Id  | Operation	   | Name | Rows  | Bytes | Cost (%CPU)| Time	  |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |	  |    14 |   420 |	6   (0)| 00:00:01 |
|*  1 |  HASH JOIN OUTER   |	  |    14 |   420 |	6   (0)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| EMP  |    14 |   238 |	3   (0)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| DEPT |	4 |    52 |	3   (0)| 00:00:01 |
---------------------------------------------------------------------------

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

   1 - access("E"."DEPTNO"="D"."DEPTNO"(+))

已选择15行。


 select  /*+ swap_join_inputs(d) use_hash(e,d)*/ e.ename,e.job,d.dname from emp e left join dept d  on e.deptno=d.deptno 

SQL> explain plan for  select  /*+ swap_join_inputs(d) use_hash(e,d)*/ e.ename,e.job,d.dname from emp e left join dept d  on e.deptno=d.deptno ;

已解释。

SQL> select * from  table(dbms_xplan.display());

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 4261033907

------------------------------------------------------------------------------
| Id  | Operation	      | Name | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------
|   0 | SELECT STATEMENT      |      |	  14 |	 420 |	   6   (0)| 00:00:01 |
|*  1 |  HASH JOIN RIGHT OUTER|      |	  14 |	 420 |	   6   (0)| 00:00:01 |
|   2 |   TABLE ACCESS FULL   | DEPT |	   4 |	  52 |	   3   (0)| 00:00:01 |
|   3 |   TABLE ACCESS FULL   | EMP  |	  14 |	 238 |	   3   (0)| 00:00:01 |
------------------------------------------------------------------------------

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

   1 - access("E"."DEPTNO"="D"."DEPTNO"(+))

已选择15行。