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包含unionall的view子查询无法展开表连接的模拟

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之前小鱼写过一些关于子查询无法展开的文章，其中主要涉及到以下几点： 1关联的列没有not null约束，在子查询中使用not in去查找（oracle 10g无法展开为子查询，oracle 11g由于有新的hash join算法已经可以），如下 SQL> select a.* from ta01 a where a.obj

之前小鱼写过一些关于子查询无法展开的文章，其中主要涉及到以下几点： 1关联的列没有not null约束，在子查询中使用not in去查找（oracle 10g无法展开为子查询，oracle 11g由于有新的hash join算法已经可以），如下


SQL> select a.* from ta01 a where a.object_id not in (select b.object_id from ta02 b)

Ta01和ta02表的object_id列上没有not null的约束
2 子查询中包含主表的关联列的谓词过滤（oracle 10g也无法展开为子查询，oracle 11g可以展开为子查询），如下
SQL> select a.* from ta01 a where a.object_id in （select b.object_id from ta02 b where a.object_type=’TABLE’）；
3 子查询中包含有下列形式的or的查询（oracle 10g同样无法展开为子查询，oracle 11g可以展开）
SQL> select a.* from ta01 a where a.object_id in (select b.object_id from ta02 b

 where object_type='TABLE') or a.object_id in (select c.object_id from ta02 c wh

ere c.object_type='INDEX');
4 子查询包含有主表和子表列的like关联，比如下列sql语句（oracle 10g和11g都无法展开为子查询）
SQL> select a.* from ta01 a where a.object_id in (select b.object_id from ta02 b

 where a.data_object_id like b.data_object_id);
http://www.eygle.com/archives/2013/04/2013_oracle_dtcc_dbsnake.html
eygle这篇文章里面又提到了一个比较常见的子查询无法展开的case，借鉴作者的案例进行一点简单的模拟来进行验证。
SQL> select * from v$version;
BANNER

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

Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi

PL/SQL Release 10.2.0.4.0 - Production

CORE    10.2.0.4.0      Production

TNS for 64-bit Windows: Version 10.2.0.4.0 - Production

NLSRTL Version 10.2.0.4.0 - Production
SQL> create table ta01 as select * from dba_objects;
Table created.
SQL> create table ta02 as select * from dba_objects;
Table created.
SQL> create table tb01 as select * from dba_objects;
Table created.
SQL> create table tb02 as select * from dba_objects;
Table created.
SQL> create view ta_view as

  2  select object_id,data_object_id,object_type from ta01 union all

  3  select object_id,data_object_id,object_type from ta02;
View created.
SQL> create view tb_view as

  2  select object_id,data_object_id,object_type from tb01 union all

  3  select object_id,data_object_id,object_type from tb02;
View created.
SQL> select a.* from ta_view a where a.object_id in (select b.object_id from tb_

view b where b.object_type='TABLE');
PLAN_TABLE_OUTPUT

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

------------------------------------------------------------
Plan hash value: 3623909176
--------------------------------------------------------------------------------
| Id  | Operation            | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT     |         |  3738K|   131M|   617   (1)| 00:00:08 |
|*  1 |  FILTER              |         |       |       |            |          |
|   2 |   VIEW               | TA_VIEW | 88401 |  3194K|   308   (1)| 00:00:04 |
|   3 |    UNION-ALL         |         |       |       |            |          |
|   4 |     TABLE ACCESS FULL| TA01    | 42509 |  1535K|   154   (1)| 00:00:02 |
|   5 |     TABLE ACCESS FULL| TA02    | 45892 |  1658K|   154   (1)| 00:00:02 |
PLAN_TABLE_OUTPUT

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

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

|   6 |   VIEW               | TB_VIEW |    42 |  1008 |   309   (1)| 00:00:04 |
|   7 |    UNION-ALL         |         |       |       |            |          |
|*  8 |     TABLE ACCESS FULL| TB01    |    17 |   408 |   154   (1)| 00:00:02 |
|*  9 |     TABLE ACCESS FULL| TB02    |    25 |   600 |   154   (1)| 00:00:02 |
--------------------------------------------------------------------------------
Predicate Information (identified by operation id):

---------------------------------------------------
   1 - filter( EXISTS (SELECT /*+ */ 0 FROM  ( (SELECT /*+ */

              "OBJECT_ID" "OBJECT_ID","DATA_OBJECT_ID" "DATA_OBJECT_ID","OBJECT_

TYPE"
PLAN_TABLE_OUTPUT

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

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

              "OBJECT_TYPE" FROM SYS."TB01" "TB01" WHERE "OBJECT_ID"=:B1 AND

              "OBJECT_TYPE"='TABLE') UNION ALL  (SELECT /*+ */ "OBJECT_ID"

              "OBJECT_ID","DATA_OBJECT_ID" "DATA_OBJECT_ID","OBJECT_TYPE"

              "OBJECT_TYPE" FROM SYS."TB02" "TB02" WHERE "OBJECT_ID"=:B2 AND

              "OBJECT_TYPE"='TABLE')) "B"))

   8 - filter("OBJECT_ID"=:B1 AND "OBJECT_TYPE"='TABLE')

   9 - filter("OBJECT_ID"=:B1 AND "OBJECT_TYPE"='TABLE')
Note

-----

   - dynamic sampling used for this statement
33 rows selected.
Statistics

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

        146  recursive calls

          0  db block gets

  136371691  consistent gets

          0  physical reads

          0  redo size

      83259  bytes sent via SQL*Net to client

       2868  bytes received via SQL*Net from client

        218  SQL*Net roundtrips to/from client

          0  sorts (memory)

          0  sorts (disk)

       3247  rows processed
这里由于主查询和子查询的表都是两个表相关联的视图，这个导致in之后的括号内的子查询并不是一个常量的集合，所以oracle这里没有对该子查询展开为表连接。
而我们可以改写为下列的sql语句，但是这里好像结果集不一样，这个是因为我们选取的表不是1对1引起的，这个不在我们考虑的范围内。

SQL> SELECT a.*

  2    FROM ta_view a,

  3         (SELECT object_id

  4            FROM tb_view

  5           WHERE object_type = 'TABLE') b

  6   WHERE a.object_id = b.object_id;
6494 rows selected.
Execution Plan

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

Plan hash value: 48097912
--------------------------------------------------------------------------------
| Id  | Operation            | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT     |         |  3328K|   158M|   640   (5)| 00:00:08 |
|*  1 |  HASH JOIN           |         |  3328K|   158M|   640   (5)| 00:00:08 |
|   2 |   VIEW               | TB_VIEW |  3306 | 42978 |   309   (1)| 00:00:04 |
|   3 |    UNION-ALL         |         |       |       |            |          |
|*  4 |     TABLE ACCESS FULL| TB01    |  1756 | 24584 |   154   (1)| 00:00:02 |
|*  5 |     TABLE ACCESS FULL| TB02    |  1550 | 21700 |   154   (1)| 00:00:02 |
|   6 |   VIEW               | TA_VIEW |   100K|  3637K|   308   (1)| 00:00:04 |
|   7 |    UNION-ALL         |         |       |       |            |          |
|   8 |     TABLE ACCESS FULL| TA01    | 50333 |   786K|   154   (1)| 00:00:02 |
|   9 |     TABLE ACCESS FULL| TA02    | 50334 |   786K|   154   (1)| 00:00:02 |
--------------------------------------------------------------------------------
Predicate Information (identified by operation id):

---------------------------------------------------
   1 - access("A"."OBJECT_ID"="OBJECT_ID")

   4 - filter("OBJECT_TYPE"='TABLE')

   5 - filter("OBJECT_TYPE"='TABLE')
Statistics

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

       1083  recursive calls

          0  db block gets

       3412  consistent gets

       2782  physical reads

        196  redo size

     139022  bytes sent via SQL*Net to client

       5244  bytes received via SQL*Net from client

        434  SQL*Net roundtrips to/from client

         31  sorts (memory)

          0  sorts (disk)

       6494  rows processed
当然如果业务也是1对多，那么这个改写是不符合业务逻辑的，那么是否就不能进行改写了，其实也不是这样的，我们只需要在构造的这个表中加上一个distinct去掉b表的重复的值，这样不就是类似为半连接了吗。

SQL> SELECT  a.*

  2    FROM ta_view a,

  3         (SELECT distinct object_id

  4            FROM tb_view

  5           WHERE object_type = 'TABLE') b

  6   WHERE a.object_id = b.object_id;
3247 rows selected.
Execution Plan

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

Plan hash value: 1607119383
--------------------------------------------------------------------------------

--

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

 |

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

--

|   0 | SELECT STATEMENT       |         |  3328K|   158M|   642   (5)| 00:00:08

 |

|*  1 |  HASH JOIN             |         |  3328K|   158M|   642   (5)| 00:00:08

 |

|   2 |   VIEW                 |         |  3306 | 42978 |   310   (2)| 00:00:04

 |

|   3 |    HASH UNIQUE         |         |  3306 | 42978 |   310   (2)| 00:00:04

 |

|   4 |     VIEW               | TB_VIEW |  3306 | 42978 |   309   (1)| 00:00:04

 |

|   5 |      UNION-ALL         |         |       |       |            |

 |

|*  6 |       TABLE ACCESS FULL| TB01    |  1756 | 24584 |   154   (1)| 00:00:02

 |

|*  7 |       TABLE ACCESS FULL| TB02    |  1550 | 21700 |   154   (1)| 00:00:02

 |

|   8 |   VIEW                 | TA_VIEW |   100K|  3637K|   308   (1)| 00:00:04

 |

|   9 |    UNION-ALL           |         |       |       |            |

 |

|  10 |     TABLE ACCESS FULL  | TA01    | 50333 |   786K|   154   (1)| 00:00:02

 |

|  11 |     TABLE ACCESS FULL  | TA02    | 50334 |   786K|   154   (1)| 00:00:02

 |

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

--
Predicate Information (identified by operation id):

---------------------------------------------------
   1 - access("A"."OBJECT_ID"="B"."OBJECT_ID")

   6 - filter("OBJECT_TYPE"='TABLE')

   7 - filter("OBJECT_TYPE"='TABLE')
Statistics

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

         15  recursive calls

          0  db block gets

       3007  consistent gets

          0  physical reads

          0  redo size

      83259  bytes sent via SQL*Net to client

       2868  bytes received via SQL*Net from client

        218  SQL*Net roundtrips to/from client

          0  sorts (memory)

          0  sorts (disk)

       3247  rows processed
关于我们常见的select a.* from a,b where a.id=b.id和select a.* from a where a.id in (select b.id from b)这两种查询，在业务层面有不同的是如果b表没有重复的id，那么这个查询业务逻辑是相同的，而如果b表有重复的，子查询是hash join的半连接方式，会对b.id进行去重，所以如果b.id存在多个重复值，可能会引起查询结果不一致。
并不是说包含union all的veiw会引起子查询无法展开为表连接，如上单个union all的view是不会影响子查询展开为表连接的。

SQL> select a.* from ta01 a where a.object_id in (select b.object_id from tb_vie

w b where b.object_type='TABLE');
1623 rows selected.
Execution Plan

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

Plan hash value: 1785931674
--------------------------------------------------------------------------------

--

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

 |

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

--

|   0 | SELECT STATEMENT      |          |     1 |   190 |   464   (2)| 00:00:06

 |

|*  1 |  HASH JOIN RIGHT SEMI |          |     1 |   190 |   464   (2)| 00:00:06

 |

|   2 |   VIEW                | VW_NSO_1 |  4229 | 54977 |   309   (1)| 00:00:04

 |

|   3 |    VIEW               | TB_VIEW  |  4229 |    99K|   309   (1)| 00:00:04

 |

|   4 |     UNION-ALL         |          |       |       |            |

 |

|*  5 |      TABLE ACCESS FULL| TB01     |  1692 | 40608 |   154   (1)| 00:00:02

 |

|*  6 |      TABLE ACCESS FULL| TB02     |  2537 | 60888 |   154   (1)| 00:00:02

 |

|   7 |   TABLE ACCESS FULL   | TA01     | 42509 |  7347K|   154   (1)| 00:00:02

 |

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

--
Predicate Information (identified by operation id):

---------------------------------------------------
   1 - access("A"."OBJECT_ID"="$nso_col_1")

   5 - filter("OBJECT_TYPE"='TABLE')

   6 - filter("OBJECT_TYPE"='TABLE')
Note

-----

   - dynamic sampling used for this statement
Statistics

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

         53  recursive calls

          0  db block gets

       3166  consistent gets

          0  physical reads

          0  redo size

      85130  bytes sent via SQL*Net to client

       1680  bytes received via SQL*Net from client

        110  SQL*Net roundtrips to/from client

          3  sorts (memory)

          0  sorts (disk)

       1623  rows processed
而如果我们换到oracle 11.2.0.1的版本，再来看看包含两个union all的view的子查询是否能够展开

SQL> select * from v$version;
BANNER

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

Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production

PL/SQL Release 11.2.0.1.0 - Production

CORE    11.2.0.1.0      Production

TNS for Linux: Version 11.2.0.1.0 - Production

NLSRTL Version 11.2.0.1.0 – Production
SQL> select a.* from ta_view a where a.object_id in (select b.object_id from tb_view b where b.object_type='TABLE');
7629 rows selected.
Execution Plan

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

Plan hash value: 1656093151
-----------------------------------------------------------------------------------

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

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

|   0 | SELECT STATEMENT       |          |  6779K|   323M|  1206   (4)| 00:00:15 |

|*  1 |  HASH JOIN             |          |  6779K|   323M|  1206   (4)| 00:00:15 |

|   2 |   VIEW                 | VW_NSO_1 |  4191 | 54483 |   586   (1)| 00:00:08 |

|   3 |    HASH UNIQUE         |          |  4191 | 54483 |   586   (1)| 00:00:08 |

|   4 |     VIEW               | TB_VIEW  |  4191 | 54483 |   585   (1)| 00:00:08 |

|   5 |      UNION-ALL         |          |       |       |            |          |

|*  6 |       TABLE ACCESS FULL| TB01     |  2036 | 48864 |   293   (1)| 00:00:04 |

|*  7 |       TABLE ACCESS FULL| TB02     |  2155 | 51720 |   292   (1)| 00:00:04 |

|   8 |   VIEW                 | TA_VIEW  |   161K|  5845K|   585   (1)| 00:00:08 |

|   9 |    UNION-ALL           |          |       |       |            |          |

|  10 |     TABLE ACCESS FULL  | TA01     | 82194 |  2969K|   292   (1)| 00:00:04 |

|  11 |     TABLE ACCESS FULL  | TA02     | 79581 |  2875K|   292   (1)| 00:00:04 |

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

---------------------------------------------------
   1 - access("A"."OBJECT_ID"="OBJECT_ID")

   6 - filter("OBJECT_TYPE"='TABLE')

   7 - filter("OBJECT_TYPE"='TABLE')
Note

-----

   - dynamic sampling used for this statement (level=2)
Statistics

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

         63  recursive calls

          0  db block gets

       5917  consistent gets

       3072  physical reads

          0  redo size

     200965  bytes sent via SQL*Net to client

       6108  bytes received via SQL*Net from client

        510  SQL*Net roundtrips to/from client

          0  sorts (memory)

          0  sorts (disk)

       7629  rows processed
这里oracle选择了将子查询展开为了表连接，优化器确实在做着很多的改变，这些改变需要我们通过文档 测试用例和实际的案例来验证，可以这么说脱离了oracle的版本来谈性能优化 sql调优其实往往是不严谨的。

最近注册了朋友介绍的一个论坛 http://www.bi168.cn/forum.php ，之前也注册了很多论坛比如itpub、otn、ask maclean等等，都没有怎么过多的去关注论坛的东西，记得maclean liu说过每天能遇见的案例是有限的，但是网络的同行遇见的case确是很多的，如果能够将别人遇见的模拟理解解决那么这个就是自己的。

原文地址：包含union all的view子查询无法展开表连接的模拟, 感谢原作者分享。

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包含unionall的view子查询无法展开表连接的模拟

之前小鱼写过一些关于子查询无法展开的文章，其中主要涉及到以下几点： 1关联的列没有not null约束，在子查询中使用not in去查找（oracle 10g无法展开为子查询，oracle 11g由于有新的hash join算法已经可以），如下 SQL> select a.* from ta01 a where a.obj之前小鱼写过一些关于子查询无法展开的文章，其中主要涉及到以下几点： 1关联的列没有not null约束，在子查询中使用not in去查找（oracle 10g无法展开为子查询，oracle 11g由...

Case：MySQL使用left join的时候or改写成union可以提高效率

(1)优化前：使用or的时候，SQL执行时间1.47smysql> select e.emp_no,e.first_name,d.dept_no,d.from_date,d.to_date from employees e left join dept_emp d on e.emp_no=d.emp_no where e.emp_no=32000 or d.from_date=1996-11-24; 58 rows in set (1.47 sec)mysql> desc select e.emp_no,e.first_name,d.dept_no,d.from_date,d.to_date from employees e left join dept_emp d on e.emp_no=d.emp_no where e.emp_no=32000 or d.f...

MysqlUnion实例_MySQL【代码】

前提，是每个查询结果集的列数要一样，类型要一样SELECT g.goods_id FROM ( SELECT gr.`GOODS_ID`,COUNT(gr.`GOODS_ID`) num FROM rkgl_goods_repertory gr JOIN rkgl_repertory r ON r.`ID`=gr.`REPERTORY_ID` JOIN spgl_goods g ON g.`ID`=gr.`GOODS_ID` JOIN spgl_brand b ON b.`ID`=g.`BRAND_ID` JOIN spgl_goods_type gt ON gt.`ID`=g.`GOODS_TYPE_ID` WHERE r.`USER_ID`=36 AND g.`IS_DELETE`=FALSE AND gt.`IS_DELETE`=FALS...

MySQL UNION ALL如何运行agregate函数？【代码】

我有一些SQL代码,它正是我想要它的工作方式：select 10 as number, "Checklist 10 Foo" as name, max(id), max(ts) as max_ts, callsign, max(time_hint_utc), count(*) from checklist_10 union all select 11 as number, "Checklist 11 Bar" as name, max(id), max(ts) as max_ts, callsign, max(time_hint_utc), count(*) from checklist_11 union all select 12 as number, "Checklist 12 Baz" as name, max(id), max(ts) as m...

Mysql：The Merge Storage Engine：类【union all】联合视图存储引擎

16.7 The MERGE Storage Engine 16.7.2 merge table problemsThe MERGE storage engine, also known as the MRG_MyISAM engine, is a collection of identical MyISAM tables that can be used as one. “Identical” means that all tables have identical column data types and index information. You cannot merge MyISAM tables in which the columns are listed in a different order, do not have exactly the same data t...

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