嵌套循环外连接 无法指定驱动表

嵌套循环 外连接改变驱动表:


 select  /*+ LEADING(e) use_nl(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  /*+ LEADING(e) use_nl(e,d)*/ e.ename,e.job,d.dname from emp e left join dept d  on e.deptno=d.deptno   2  ;

已解释。

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

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 1330733389

----------------------------------------------------------------------------------------
| Id  | Operation		     | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT	     |	       |    14 |   420 |    17	 (0)| 00:00:01 |
|   1 |  NESTED LOOPS OUTER	     |	       |    14 |   420 |    17	 (0)| 00:00:01 |
|   2 |   TABLE ACCESS FULL	     | EMP     |    14 |   238 |     3	 (0)| 00:00:01 |
|   3 |   TABLE ACCESS BY INDEX ROWID| DEPT    |     1 |    13 |     1	 (0)| 00:00:01 |
|*  4 |    INDEX UNIQUE SCAN	     | DEPT_PK |     1 |       |     0	 (0)| 00:00:01 |
----------------------------------------------------------------------------------------

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

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

已选择16行。


SQL> explain plan for select  /*+ LEADING(d) use_nl(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: 1330733389

----------------------------------------------------------------------------------------
| Id  | Operation		     | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT	     |	       |    14 |   420 |    17	 (0)| 00:00:01 |
|   1 |  NESTED LOOPS OUTER	     |	       |    14 |   420 |    17	 (0)| 00:00:01 |
|   2 |   TABLE ACCESS FULL	     | EMP     |    14 |   238 |     3	 (0)| 00:00:01 |
|   3 |   TABLE ACCESS BY INDEX ROWID| DEPT    |     1 |    13 |     1	 (0)| 00:00:01 |
|*  4 |    INDEX UNIQUE SCAN	     | DEPT_PK |     1 |       |     0	 (0)| 00:00:01 |
----------------------------------------------------------------------------------------

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

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

已选择16行。


嵌套循环外连接的时候,无法修改驱动表