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  • 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。
    
    

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  • 原文地址:https://www.cnblogs.com/hzcya1995/p/13352332.html
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