left join 关联条件位置

select e.last_name, e.department_id, d.department_name
  from hr.employees e
  left outer join hr.departments d on (e.department_id = d.department_id);

select e.last_name, e.department_id, d.department_name
  from hr.employees e
  left outer join hr.departments d on ( d.department_id=e.department_id );

SQL> select e.last_name, e.department_id, d.department_name
  from hr.employees e
  left outer join hr.departments d on (e.department_id = d.department_id);  2    3  

107 rows selected.

Execution Plan
----------------------------------------------------------
Plan hash value: 2296652067

----------------------------------------------------------------------------------
| Id  | Operation	   | Name	 | Rows  | Bytes | Cost (%CPU)| Time	 |
----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |		 |   107 |  2889 |     7  (15)| 00:00:01 |
|*  1 |  HASH JOIN OUTER   |		 |   107 |  2889 |     7  (15)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| EMPLOYEES	 |   107 |  1177 |     3   (0)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| DEPARTMENTS |    27 |   432 |     3   (0)| 00:00:01 |
----------------------------------------------------------------------------------

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

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

SQL> select e.last_name, e.department_id, d.department_name
  from hr.employees e
  left outer join hr.departments d on ( d.department_id=e.department_id );  2    3  

107 rows selected.

Execution Plan
----------------------------------------------------------
Plan hash value: 2296652067

----------------------------------------------------------------------------------
| Id  | Operation	   | Name	 | Rows  | Bytes | Cost (%CPU)| Time	 |
----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |		 |   107 |  2889 |     7  (15)| 00:00:01 |
|*  1 |  HASH JOIN OUTER   |		 |   107 |  2889 |     7  (15)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| EMPLOYEES	 |   107 |  1177 |     3   (0)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| DEPARTMENTS |    27 |   432 |     3   (0)| 00:00:01 |
----------------------------------------------------------------------------------

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

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

 (e.department_id = d.department_id)和( d.department_id=e.department_id )位置没有影响。