Oracle not exists的等價寫法

Oracle not exists的等價寫法

not exists可以改為left join + is null，可以看到改寫前後執行計畫一樣，消耗資源一樣，說明完全等價。

SQL> drop table test purge;

SQL> drop table test1 purge;
SQL> create table test as select * from dba_objects;
SQL> create table test1 as select * from dba_objects;
SQL> delete from test1 where rownum < 10;
SQL> commit;

SQL> select count(1) from test t where not exists(
    select 1 from test1 t1 where t1.object_id=t.object_id
    );
  COUNT(1)
----------
        11
SQL> select count(1) from test t,test1 t1 where t.object_id=t1.object_id(+)
    and t1.object_id is null;
  COUNT(1)
----------
        11
SQL> select * from test t where not exists(
    select 1 from test1 t1 where t1.object_id=t.object_id
    )
    minus
    select t.* from test t,test1 t1 where t.object_id=t1.object_id(+)
    and t1.object_id is null;
未選定行

SQL> select t.* from test t,test1 t1 where t.object_id=t1.object_id(+)
    and t1.object_id is null
    minus
    select * from test t where not exists(
    select 1 from test1 t1 where t1.object_id=t.object_id
    );
未選定行

SQL> set autotrace traceonly
SQL> select t.* from test t where not exists(
    select 1 from test1 t1 where t1.object_id=t.object_id
    );
已選擇11行。
執行計畫
----------------------------------------------------------
Plan hash value: 2726816538
--------------------------------------------------------------------------------------
| Id  | Operation            | Name  | Rows  | Bytes |TempSpc| Cost (%CPU)| Time    |
--------------------------------------------------------------------------------------
|  0 | SELECT STATEMENT    |      | 72877 |    15M|      |  1109  (1)| 00:00:16 |
|*  1 |  HASH JOIN RIGHT ANTI|      | 72877 |    15M|  1520K|  1109  (1)| 00:00:16 |
|  2 |  TABLE ACCESS FULL  | TEST1 | 61874 |  785K|      |  196  (1)| 00:00:03 |
|  3 |  TABLE ACCESS FULL  | TEST  | 72877 |    14M|      |  197  (2)| 00:00:03 |
--------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
  1 - access("T1"."OBJECT_ID"="T"."OBJECT_ID")
Note
-----
  - dynamic sampling used for this statement (level=2)
統計資訊
----------------------------------------------------------
          7  recursive calls
          0  db block gets
      1142  consistent gets
          0  physical reads
          0  redo size
      1577  bytes sent via SQL*Net to client
        337  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
        11  rows processed
SQL> select t.* from test t,test1 t1 where t.object_id=t1.object_id(+)
  2  and t1.object_id is null;
已選擇11行。
執行計畫
----------------------------------------------------------
Plan hash value: 2726816538
--------------------------------------------------------------------------------------
| Id  | Operation            | Name  | Rows  | Bytes |TempSpc| Cost (%CPU)| Time    |
--------------------------------------------------------------------------------------
|  0 | SELECT STATEMENT    |      | 72877 |    15M|      |  1109  (1)| 00:00:16 |
|*  1 |  HASH JOIN RIGHT ANTI|      | 72877 |    15M|  1520K|  1109  (1)| 00:00:16 |
|  2 |  TABLE ACCESS FULL  | TEST1 | 61874 |  785K|      |  196  (1)| 00:00:03 |
|  3 |  TABLE ACCESS FULL  | TEST  | 72877 |    14M|      |  197  (2)| 00:00:03 |
--------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
  1 - access("T"."OBJECT_ID"="T1"."OBJECT_ID")
Note
-----
  - dynamic sampling used for this statement (level=2)
統計資訊
----------------------------------------------------------
          7  recursive calls
          0  db block gets
      1142  consistent gets
          0  physical reads
          0  redo size
      1577  bytes sent via SQL*Net to client
        337  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
        11  rows processed

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