Oracle技术之Oracle查询重写对全外连接无效(一)

测试发现，Oracle不支持全外连接的查询重写，即使物化视图和查询语句完全匹配。

在10g中测试发现对于全外连接，创建语句一致的物化视图也无法利用查询重新功能：

[oracle@yans1 ~]$ sqlplus test/test

SQL*Plus: Release10.2.0.3.0 - Production on星期一10月18 12:16:47 2010

Copyright (c) 1982, 2006, Oracle.  All Rights Reserved.

Connected to:

Oracle Database10gEnterprise Edition Release10.2.0.3.0 - 64bit Production

With the Partitioning, OLAP and Data Mining options

SQL> SET PAGES 100 LINES 120

SQL> SHOW PARAMETER QUERY

NAME                                 TYPE        VALUE

------------------------------------ ----------- ------------------------------

query_rewrite_enabled                string      TRUE

query_rewrite_integrity              string      enforced

SQL> CREATE MATERIALIZED VIEW MV_T1_FULL_JOIN_T2  

 2  ENABLE QUERY REWRITE AS

 3  SELECT T1.ID ID1, T2.ID ID2

 4  FROM T1 FULL OUTER JOIN T2

 5  ON T1.ID = T2.ID;

Materialized view created.

SQL> SET AUTOT ON

SQL> SELECT T1.ID ID1, T2.ID ID2

 2  FROM T1 FULL OUTER JOIN T2

 3  ON T1.ID = T2.ID;

      ID1        ID2

---------- ----------

        2          2

        3          3

        4          4

        5          5

        6          6

        7          7

        8          8

        1

        0

                  10

                   9

11 rows selected.

Execution Plan

----------------------------------------------------------

Plan hash value: 2841162349

-----------------------------------------------------------------------------

| Id  | Operation            | Name | Rows  | Bytes | Cost (%CPU)| Time     |

-----------------------------------------------------------------------------

|   0 | SELECT STATEMENT     |      |    10 |   260 |    13   (8)| 00:00:01 |

|   1 |  VIEW                |      |    10 |   260 |    13   (8)| 00:00:01 |

|   2 |   UNION-ALL          |      |       |       |            |          |

|*  3 |    HASH JOIN OUTER   |      |     9 |   234 |     7  (15)| 00:00:01 |

|   4 |     TABLE ACCESS FULL| T1   |     9 |   117 |     3   (0)| 00:00:01 |

|   5 |     TABLE ACCESS FULL| T2   |     9 |   117 |     3   (0)| 00:00:01 |

|*  6 |    HASH JOIN ANTI    |      |     1 |    26 |     7  (15)| 00:00:01 |

|   7 |     TABLE ACCESS FULL| T2   |     9 |   117 |     3   (0)| 00:00:01 |

|   8 |     TABLE ACCESS FULL| T1   |     9 |   117 |     3   (0)| 00:00:01 |

-----------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

  3 - access("T1"."ID"="T2"."ID"(+))

  6 - access("T1"."ID"="T2"."ID")

Note

-----

  - dynamic sampling used for this statement

Statistics

----------------------------------------------------------

      1551  recursive calls

         0  db block gets

       427  consistent gets

        10  physical reads

         0  redo size

       720  bytes sent via SQL*Net to client

       492  bytes received via SQL*Net from client

         2  SQL*Net roundtrips to/from client

        47  sorts (memory)

         0  sorts (disk)

        11  rows processed

SQL> SELECT /*+ REWRITE(MV_T1_FULL_JOIN_T2) */ T1.ID ID1, T2.ID ID2

 2  FROM T1 FULL OUTER JOIN T2

 3  ON T1.ID = T2.ID;

      ID1        ID2

---------- ----------

        2          2

        3          3

        4          4

        5          5

        6          6

        7          7

        8          8

        1

        0

                  10

                   9

11 rows selected.

Execution Plan

----------------------------------------------------------

Plan hash value: 2841162349

-----------------------------------------------------------------------------

| Id  | Operation            | Name | Rows  | Bytes | Cost (%CPU)| Time     |

-----------------------------------------------------------------------------

|   0 | SELECT STATEMENT     |      |    10 |   260 |    13   (8)| 00:00:01 |

|   1 |  VIEW                |      |    10 |   260 |    13   (8)| 00:00:01 |

|   2 |   UNION-ALL          |      |       |       |            |          |

|*  3 |    HASH JOIN OUTER   |      |     9 |   234 |     7  (15)| 00:00:01 |

|   4 |     TABLE ACCESS FULL| T1   |     9 |   117 |     3   (0)| 00:00:01 |

|   5 |     TABLE ACCESS FULL| T2   |     9 |   117 |     3   (0)| 00:00:01 |

|*  6 |    HASH JOIN ANTI    |      |     1 |    26 |     7  (15)| 00:00:01 |

|   7 |     TABLE ACCESS FULL| T2   |     9 |   117 |     3   (0)| 00:00:01 |

|   8 |     TABLE ACCESS FULL| T1   |     9 |   117 |     3   (0)| 00:00:01 |

-----------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

  3 - access("T1"."ID"="T2"."ID"(+))

  6 - access("T1"."ID"="T2"."ID")

Note

-----

  - dynamic sampling used for this statement

Statistics

----------------------------------------------------------

        13  recursive calls

         0  db block gets

        61  consistent gets

         0  physical reads

         0  redo size

       720  bytes sent via SQL*Net to client

       492  bytes received via SQL*Net from client

         2  SQL*Net roundtrips to/from client

         4  sorts (memory)

         0  sorts (disk)

        11  rows processed

同样在11g中存在同样的问题，创建REWRITE_TABLE，检查无法查询重写的原因：

SQL> @?/rdbms/admin/utlxrw

表已创建。

SQL> begin

 2  dbms_mview.explain_rewrite('SELECT T1.ID, T2.ID

 3  FROM T1 FULL OUTER JOIN T2

 4  ON T1.ID = T2.ID');

 5  end;

 6  /

PL/SQL过程已成功完成。

SQL> select MESSAGE from REWRITE_TABLE;

MESSAGE

-------------------------------------------------------------------------------------------

QSM-01150:未重写查询

QSM-01219:未找到合适的实体化视图来重写此查询

QSM-01263:如果查询引用了字典表或视图,则无法执行查询重写

根据表中的信息查询metalink，虽然找到类似的bug，但是这个bug在11gr2中已经被修正，而当前的sql在11gr2中依然存在。看来又是一个隐藏的bug。

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