【书评:Oracle查询优化改写】第三章

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【书评:Oracle查询优化改写】第三章_结构图

一.1 导读

各位技术爱好者,看完本文后,你可以掌握如下的技能,也可以学到一些其它你所不知道的知识,~O(∩_∩)O~:

① 隐含参数 _b_tree_bitmap_plans介绍

② 11g新特性Native Full Outer Join

本文如有错误或不完善的地方请大家多多指正,ITPUB留言或QQ皆可,您的批评指正是我写作的最大动力。

一.2 实验环境介绍

oracle:11.2.0.3  、8.1.7.0.0

OS: RHEL6.5

一.3 前言

前2章的链接参考相关连接:

【书评:Oracle查询优化改写】第一章 http://blog.itpub.net/26736162/viewspace-1652985/

【书评:Oracle查询优化改写】第二章http://blog.itpub.net/26736162/viewspace-1654252/

昨天晚上(5.14)看完了《Oracle查询优化改写》的第三章,不得不说下这本书里边代码的排版有很大问题,格式老是不对齐,尤其是执行计划的格式,可能是印刷的时候出现的问题吧,不说这个了。这个第三章主要是讲多表的关联,包括各种连接的写法,如左联、右联,以及过滤条件错误地放在WHERE里会有什么影响;当数据有重复值时要直接关联还是分组汇总后再关联。

第 3 章 操作多个表

3.1 UNION ALL 与空字符串

3.2 UNION 与 OR

3.3 组合相关的行

3.4 IN、EXISTS 和 INNER JOIN

3.5 INNER JOIN、LEFT JOIN、RIGHT JOIN 和 FULL JOIN 解析

3.6 自关联

3.7 NOT IN、NOT EXISTS 和 LEFT JOIN

3.8 外连接中的条件不要乱放

3.9 检测两个表中的数据及对应数据的条数是否相同

3.10 聚集与内连接

3.11 聚集与外连接

3.12 从多个表中返回丢失的数据

3.13 多表查询时的空值处理

下边我就针对一些重点,或者说是我自己也不是很懂的部分做做研究吧。

一.4 隐含参数 _b_tree_bitmap_plans 实验

一.4.1 简介

该参数为隐含参数,是指是否将索引转换为bitmap索引然后执行,在oracle9i之前默认值为false,之后的默认值为true。可以这样认为,如有两个字段A,B都有btree索引,oracle有可能将这两个索引转换成bitmap索引然后做and操作得出结果集。如果改为false就会选用其中的一个索引,走btree的索引,我们可以将该参数在session或系统级别设置为false,也可以加hint   /*+ opt_param('_b_tree_bitmap_plans', 'false') */  来实现禁用该参数。

· symptom: Execution plan operation shows bitmap conversion from rowids

· symptom: No bitmap indexes

· symptom: Execution plan shows BITMAP CONVERSION

· cause: In 7.3.4 and in 8.1.7 default value of _b_tree_bitmap_plans is FALSE 
whereas as of 9.0.1 (and 9.2) the default value is TRUE When _b_tree_bitmap_plans set to true (advice not to change the default setting 
yourself) the optimizer is allowed to produce bitmap plans for normal b*tree 
indexes even if no bitmap indexes set.

相关的执行计划中可能转换为如下的形式:

(1)BITMAP CONVERSION FROM ROWIDS

将一批数据记录的ROWID映射为位图。

对于普通B*树索引,Oracle也可以将数据记录的ROWID映射成一个位图,然后进行位图操作。进行这样的转换需要将系统参数_b_tree_bitmap_plans设置为TRUE。

(2)BITMAP CONVERSION TO ROWIDS

将位图映射为ROWID。在一个位图键值中,包含了一批数据记录的起始地址和结束地址,且这批记录是连续的,因此位图中的每一个位就按序对应了一条数据记录。

(3)BITMAP OR

对位图进行“或”(OR)操作。在查询的过滤条件中,如果位图索引字段直接的关系是“或”,可以通过BITMAP OR来判断位图所映射的一批数据记录是否满足条件。

eygle大师的一个例子:

http://www.eygle.com/archives/2011/12/bitmap_conversion_cpu.html

一.4.2 11g情况下

[root@rhel6_lhr ~]# su - oracle

[oracle@rhel6_lhr ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.3.0 Production on Fri May 10:16:10 2015

Copyright (c) 1982, 2011, Oracle.  All rights reserved.

Connected to:

Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production

With the Partitioning, Automatic Storage Management, OLAP, Data Mining

and Real Application Testing options

10:16:10 SQL>

10:16:10 SQL> conn lhr/lhr

Connected.

10:16:10 SQL> create table emp_bk as select * from scott.emp;

Table created.

Elapsed: 00:00:03.43

10:16:15 SQL> create index idx_emp_empno on emp_bk(empno);

Index created.

Elapsed: 00:00:00.05

10:19:26 SQL> create index idx_emp_ename on emp_bk(ename);

Index created.

Elapsed: 00:00:00.04

10:20:48 SQL> explain plan for select empno,ename from emp_bk where empno=7788 or ename='SCOTT';

Explained.

Elapsed: 00:00:00.09

10:20:56 SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT

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

Plan hash value: 4193090541

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

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

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

|   0 | SELECT STATEMENT                 |               |     1 |    20 |     2   (0)| 00:00:01 |

|   1 |  TABLE ACCESS BY INDEX ROWID     | EMP_BK        |     1 |    20 |     2   (0)| 00:00:01 |

|   2 |   BITMAP CONVERSION TO ROWIDS    |               |       |       |            |          |

|   3 |    BITMAP OR                     |               |       |       |            |          |

|   4 |     BITMAP CONVERSION FROM ROWIDS|               |       |       |            |          |

|*  5 |      INDEX RANGE SCAN            | IDX_EMP_EMPNO |       |       |     1   (0)| 00:00:01 |

|   6 |     BITMAP CONVERSION FROM ROWIDS|               |       |       |            |          |

|*  7 |      INDEX RANGE SCAN            | IDX_EMP_ENAME |       |       |     1   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

   5 - access("EMPNO"=7788)

   7 - access("ENAME"='SCOTT')

Note

-----

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

24 rows selected.

Elapsed: 00:00:00.52

10:24:06 SQL> conn / as sysdba

Connected.

Elapsed: 00:00:00.03

10:24:34 SQL> set pagesize 9999

10:24:41 SQL> set line 9999

10:24:41 SQL> col NAME format a30

10:24:41 SQL> col KSPPDESC format a50

10:24:41 SQL> col KSPPSTVL format a20

10:24:42 SQL> SELECT a.INDX,

10:24:42   2         a.KSPPINM NAME,

10:24:42   3         a.KSPPDESC,

10:24:42   4         b.KSPPSTVL

10:24:42   5  FROM   x$ksppi  a,

10:24:42   6         x$ksppcv b

10:24:42   7  WHERE  a.INDX = b.INDX

10:24:42   8  and lower(a.KSPPINM) like  lower('%?meter%');

Enter value for parameter: _b_tree_bitmap_plans

old   8: and lower(a.KSPPINM) like  lower('%?meter%')

new   8: and lower(a.KSPPINM) like  lower('%_b_tree_bitmap_plans%')

      INDX NAME                           KSPPDESC                                           KSPPSTVL

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

      1910 _b_tree_bitmap_plans           enable the use of bitmap plans for tables w. only  TRUE

                                          B-tree indexes

Elapsed: 00:00:00.01

10:25:44 SQL> conn lhr/lhr

Connected.

10:26:56 SQL> alter session set "_b_tree_bitmap_plans" = false;

Session altered.

Elapsed: 00:00:00.00

10:27:01 SQL> show parameter _b_tree_bitmap_plans

NAME                                 TYPE        VALUE

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

_b_tree_bitmap_plans                 boolean     FALSE

10:27:05 SQL> explain plan for select empno,ename from emp_bk where empno=7788 or ename='SCOTT';

Explained.

Elapsed: 00:00:00.01

10:27:14 SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT

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

Plan hash value: 370270337

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

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

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

|   0 | SELECT STATEMENT  |        |     1 |    20 |     3   (0)| 00:00:01 |

|*  1 |  TABLE ACCESS FULL| EMP_BK |     1 |    20 |     3   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

   1 - filter("EMPNO"=7788 OR "ENAME"='SCOTT')

Note

-----

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

17 rows selected.

Elapsed: 00:00:00.04

10:27:18 SQL> explain plan for select empno,ename from emp_bk where empno=7788

10:27:49   2  union

10:27:55   3  select empno,ename from emp_bk where ename='SCOTT';

Explained.

Elapsed: 00:00:00.00

10:28:07 SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT

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

Plan hash value: 3014579657

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

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

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

|   0 | SELECT STATEMENT              |               |     2 |    40 |     6  (67)| 00:00:01 |

|   1 |  SORT UNIQUE                  |               |     2 |    40 |     6  (67)| 00:00:01 |

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

|   3 |    TABLE ACCESS BY INDEX ROWID| EMP_BK        |     1 |    20 |     2   (0)| 00:00:01 |

|*  4 |     INDEX RANGE SCAN          | IDX_EMP_EMPNO |     1 |       |     1   (0)| 00:00:01 |

|   5 |    TABLE ACCESS BY INDEX ROWID| EMP_BK        |     1 |    20 |     2   (0)| 00:00:01 |

|*  6 |     INDEX RANGE SCAN          | IDX_EMP_ENAME |     1 |       |     1   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

   4 - access("EMPNO"=7788)

   6 - access("ENAME"='SCOTT')

Note

-----

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

23 rows selected.

Elapsed: 00:00:00.01

10:28:13 SQL> Select Name ,Value From v$parameter Where Name ='_b_tree_bitmap_plans' ;

NAME                           VALUE

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

_b_tree_bitmap_plans           FALSE

Elapsed: 00:00:00.02

10:34:06 SQL> alter session set "_b_tree_bitmap_plans" = true;

Session altered.

Elapsed: 00:00:00.00

11:19:04 SQL> explain plan for select /*+ opt_param('_b_tree_bitmap_plans', 'false') */ empno,ename from emp_bk where empno=7788 or ename='SCOTT';

Explained.

Elapsed: 00:00:00.08

11:19:22 SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT

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

Plan hash value: 370270337

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

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

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

|   0 | SELECT STATEMENT  |        |     1 |    20 |     3   (0)| 00:00:01 |

|*  1 |  TABLE ACCESS FULL| EMP_BK |     1 |    20 |     3   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

   1 - filter("EMPNO"=7788 OR "ENAME"='SCOTT')

Note

-----

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

17 rows selected.

Elapsed: 00:00:00.24

由实验可以看出,_b_tree_bitmap_plans设置为false后,emp_bk走了全表扫描,并没有走位图索引转换。

一.4.3 8i情况下

C:\Users\Administrator>sqlplus "lhr/lhr@orcl8i as sysdba"

SQL*Plus: Release 8.1.7.0.0 - Production on Mon May 18 10:44:28 2015

(c) Copyright 2000 Oracle Corporation.  All rights reserved.

Connected to:

Oracle8i Enterprise Edition Release 8.1.7.0.0 - Production

With the Partitioning option

JServer Release 8.1.7.0.0 - Production

SQL> set pagesize 9999

SQL> set line 9999

SQL> col NAME format a30

SQL> col KSPPDESC format a50

SQL> col KSPPSTVL format a20

SQL> SELECT a.INDX,

  2         a.KSPPINM NAME,

  3         a.KSPPDESC,

  4         b.KSPPSTVL

  5  FROM   x$ksppi  a,

  6         x$ksppcv b

  7  WHERE  a.INDX = b.INDX

  8  and lower(a.KSPPINM) like  lower('%?meter%');

Enter value for parameter: _b_tree_bitmap_plans

old   8: and lower(a.KSPPINM) like  lower('%?meter%')

new   8: and lower(a.KSPPINM) like  lower('%_b_tree_bitmap_plans%')

      INDX NAME                           KSPPDESC                                           KSPPSTVL

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

       348 _b_tree_bitmap_plans           enable the use of bitmap plans for tables w. only  FALSE

                                          B-tree indexes

SQL>

SQL> create table lhr.emp_bk as select * from scott.emp;

Table created.

SQL> create index lhr.idx_emp_empno on lhr.emp_bk(empno);

Index created.

SQL> create index lhr.idx_emp_ename on lhr.emp_bk(ename);

Index created.

SQL> set line 9999 pagesize 9999

SQL> set autot on;

SQL> select empno,ename from lhr.emp_bk where empno=7788 or ename='SCOTT';

     EMPNO ENAME

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

      7788 SCOTT

Execution Plan

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

          0                    SELECT STATEMENT Optimizer=CHOOSE

          1                  0   CONCATENATION

          2                  1     TABLE ACCESS (BY INDEX ROWID) OF 'EMP_BK'

          3                  2       INDEX (RANGE SCAN) OF 'IDX_EMP_ENAME' (NON-UNIQUE)

          4                  1     TABLE ACCESS (BY INDEX ROWID) OF 'EMP_BK'

          5                  4       INDEX (RANGE SCAN) OF 'IDX_EMP_EMPNO' (NON-UNIQUE)

Statistics

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

          0  recursive calls

          0  db block gets

          0  consistent gets

          0  physical reads

          0  redo size

          0  bytes sent via SQL*Net to client

          0  bytes received via SQL*Net from client

          0  SQL*Net roundtrips to/from client

          0  sorts (memory)

          0  sorts (disk)

          1  rows processed

SQL>

8i下默认为false,执行计划也完全不同。

一.5 Native Full Outer Join

关于这个特性可以参考如下文章:

http://blog.itpub.net/26736162/viewspace-1660038/

我们在10.2.0.4下测试一下:

[oracle@rhel6_lhr ~]$ sqlplus / as sysdba

SQL*Plus: Release 10.2.0.4.0 - Production on Mon May 18 11:41:13 2015

Copyright (c) 1982, 2007, Oracle.  All Rights Reserved.

Connected to an idle instance.

SQL> startup

ORACLE instance started.

Total System Global Area  448790528 bytes

Fixed Size                  2084616 bytes

Variable Size             121635064 bytes

Database Buffers          318767104 bytes

Redo Buffers                6303744 bytes

Database mounted.

Database opened.

SQL> create table lhr.emp_bk as select * from scott.emp;

Table created.

SQL> create table lhr.emp_bk as select * from scott.emp;

Table created.

SQL> set autot on;

SQL> set line 9999 pagesize 9999

SQL> select * from lhr.emp_bk a full outer join lhr.emp_bk2 b on a.empno=b.empno;

     EMPNO ENAME      JOB              MGR HIREDATE                   SAL       COMM     DEPTNO      EMPNO ENAME      JOB              MGR HIREDATE                   SAL       COMM     DEPTNO

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

      7369 SMITH      CLERK           7902 1980-12-17 00:00:00        800                    20       7369 SMITH      CLERK           7902 1980-12-17 00:00:00        800                    20

      7499 ALLEN      SALESMAN        7698 1981-02-20 00:00:00       1600        300         30       7499 ALLEN      SALESMAN        7698 1981-02-20 00:00:00       1600        300         30

      7521 WARD       SALESMAN        7698 1981-02-22 00:00:00       1250        500         30       7521 WARD       SALESMAN        7698 1981-02-22 00:00:00       1250        500         30

      7566 JONES      MANAGER         7839 1981-04-02 00:00:00       2975                    20       7566 JONES      MANAGER         7839 1981-04-02 00:00:00       2975                    20

      7654 MARTIN     SALESMAN        7698 1981-09-28 00:00:00       1250       1400         30       7654 MARTIN     SALESMAN        7698 1981-09-28 00:00:00       1250       1400         30

      7698 BLAKE      MANAGER         7839 1981-05-01 00:00:00       2850                    30       7698 BLAKE      MANAGER         7839 1981-05-01 00:00:00       2850                    30

      7782 CLARK      MANAGER         7839 1981-06-09 00:00:00       2450                    10       7782 CLARK      MANAGER         7839 1981-06-09 00:00:00       2450                    10

      7788 SCOTT      ANALYST         7566 1987-04-19 00:00:00       3000                    20       7788 SCOTT      ANALYST         7566 1987-04-19 00:00:00       3000                    20

      7839 KING       PRESIDENT            1981-11-17 00:00:00       5000                    10       7839 KING       PRESIDENT            1981-11-17 00:00:00       5000                    10

      7844 TURNER     SALESMAN        7698 1981-09-08 00:00:00       1500          0         30       7844 TURNER     SALESMAN        7698 1981-09-08 00:00:00       1500          0         30

      7876 ADAMS      CLERK           7788 1987-05-23 00:00:00       1100                    20       7876 ADAMS      CLERK           7788 1987-05-23 00:00:00       1100                    20

      7900 JAMES      CLERK           7698 1981-12-03 00:00:00        950                    30       7900 JAMES      CLERK           7698 1981-12-03 00:00:00        950                    30

      7902 FORD       ANALYST         7566 1981-12-03 00:00:00       3000                    20       7902 FORD       ANALYST         7566 1981-12-03 00:00:00       3000                    20

      7934 MILLER     CLERK           7782 1982-01-23 00:00:00       1300                    10       7934 MILLER     CLERK           7782 1982-01-23 00:00:00       1300                    10

14 rows selected.

Execution Plan

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

Plan hash value: 914601651

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

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

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

|   0 | SELECT STATEMENT     |         |    15 |  2610 |    13   (8)| 00:00:01 |

|   1 |  VIEW                |         |    15 |  2610 |    13   (8)| 00:00:01 |

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

|*  3 |    HASH JOIN OUTER   |         |    14 |  2436 |     7  (15)| 00:00:01 |

|   4 |     TABLE ACCESS FULL| EMP_BK  |    14 |  1218 |     3   (0)| 00:00:01 |

|   5 |     TABLE ACCESS FULL| EMP_BK2 |    14 |  1218 |     3   (0)| 00:00:01 |

|*  6 |    HASH JOIN ANTI    |         |     1 |   100 |     7  (15)| 00:00:01 |

|   7 |     TABLE ACCESS FULL| EMP_BK2 |    14 |  1218 |     3   (0)| 00:00:01 |

|   8 |     TABLE ACCESS FULL| EMP_BK  |    14 |   182 |     3   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

   3 - access("A"."EMPNO"="B"."EMPNO"(+))

   6 - access("A"."EMPNO"="B"."EMPNO")

Note

-----

   - dynamic sampling used for this statement

Statistics

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

        338  recursive calls

          0  db block gets

         61  consistent gets

          6  physical reads

          0  redo size

       2521  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)

         14  rows processed

SQL> select /*+ NATIVE_FULL_OUTER_JOIN */ * from lhr.emp_bk a full outer join lhr.emp_bk2 b on a.empno=b.empno;

     EMPNO ENAME      JOB              MGR HIREDATE                   SAL       COMM     DEPTNO      EMPNO ENAME      JOB              MGR HIREDATE                   SAL       COMM     DEPTNO

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

      7369 SMITH      CLERK           7902 1980-12-17 00:00:00        800                    20       7369 SMITH      CLERK           7902 1980-12-17 00:00:00        800                    20

      7499 ALLEN      SALESMAN        7698 1981-02-20 00:00:00       1600        300         30       7499 ALLEN      SALESMAN        7698 1981-02-20 00:00:00       1600        300         30

      7521 WARD       SALESMAN        7698 1981-02-22 00:00:00       1250        500         30       7521 WARD       SALESMAN        7698 1981-02-22 00:00:00       1250        500         30

      7566 JONES      MANAGER         7839 1981-04-02 00:00:00       2975                    20       7566 JONES      MANAGER         7839 1981-04-02 00:00:00       2975                    20

      7654 MARTIN     SALESMAN        7698 1981-09-28 00:00:00       1250       1400         30       7654 MARTIN     SALESMAN        7698 1981-09-28 00:00:00       1250       1400         30

      7698 BLAKE      MANAGER         7839 1981-05-01 00:00:00       2850                    30       7698 BLAKE      MANAGER         7839 1981-05-01 00:00:00       2850                    30

      7782 CLARK      MANAGER         7839 1981-06-09 00:00:00       2450                    10       7782 CLARK      MANAGER         7839 1981-06-09 00:00:00       2450                    10

      7788 SCOTT      ANALYST         7566 1987-04-19 00:00:00       3000                    20       7788 SCOTT      ANALYST         7566 1987-04-19 00:00:00       3000                    20

      7839 KING       PRESIDENT            1981-11-17 00:00:00       5000                    10       7839 KING       PRESIDENT            1981-11-17 00:00:00       5000                    10

      7844 TURNER     SALESMAN        7698 1981-09-08 00:00:00       1500          0         30       7844 TURNER     SALESMAN        7698 1981-09-08 00:00:00       1500          0         30

      7876 ADAMS      CLERK           7788 1987-05-23 00:00:00       1100                    20       7876 ADAMS      CLERK           7788 1987-05-23 00:00:00       1100                    20

      7900 JAMES      CLERK           7698 1981-12-03 00:00:00        950                    30       7900 JAMES      CLERK           7698 1981-12-03 00:00:00        950                    30

      7902 FORD       ANALYST         7566 1981-12-03 00:00:00       3000                    20       7902 FORD       ANALYST         7566 1981-12-03 00:00:00       3000                    20

      7934 MILLER     CLERK           7782 1982-01-23 00:00:00       1300                    10       7934 MILLER     CLERK           7782 1982-01-23 00:00:00       1300                    10

14 rows selected.

Execution Plan

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

Plan hash value: 2812081866

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

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

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

|   0 | SELECT STATEMENT      |          |    14 |  2436 |     7  (15)| 00:00:01 |

|   1 |  VIEW                 | VW_FOJ_0 |    14 |  2436 |     7  (15)| 00:00:01 |

|*  2 |   HASH JOIN FULL OUTER|          |    14 |  2436 |     7  (15)| 00:00:01 |

|   3 |    TABLE ACCESS FULL  | EMP_BK   |    14 |  1218 |     3   (0)| 00:00:01 |

|   4 |    TABLE ACCESS FULL  | EMP_BK2  |    14 |  1218 |     3   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

   2 - access("A"."EMPNO"="B"."EMPNO")

Note

-----

   - dynamic sampling used for this statement

Statistics

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

          7  recursive calls

          0  db block gets

         15  consistent gets

          0  physical reads

          0  redo size

       2521  bytes sent via SQL*Net to client

        492  bytes received via SQL*Net from client

          2  SQL*Net roundtrips to/from client

          2  sorts (memory)

          0  sorts (disk)

         14  rows processed

SQL> set pagesize 9999

SQL> set line 9999

SQL> col NAME format a40

SQL> col KSPPDESC format a50

SQL> col KSPPSTVL format a20

SQL> SELECT a.INDX,

  2         a.KSPPINM NAME,

  3         a.KSPPDESC,

  4         b.KSPPSTVL

  5  FROM   x$ksppi  a,

  6         x$ksppcv b

  7  WHERE  a.INDX = b.INDX

  8  and lower(a.KSPPINM) like  lower('%?meter%');

Enter value for parameter: optimizer_native_full_outer_join

old   8: and lower(a.KSPPINM) like  lower('%?meter%')

new   8: and lower(a.KSPPINM) like  lower('%optimizer_native_full_outer_join%')

      INDX NAME                           KSPPDESC                                           KSPPSTVL

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

      1318 _optimizer_native_full_outer_j execute full outer join using native implementaion off

           oin

SQL>

一.6 多表查询时候的null值处理

我们在第一篇(http://blog.itpub.net/26736162/viewspace-1652985/)中总结了一下null值特征,今天我们再来看一下多表查询的时候null值得处理。

一.6.1 情形一:

若子查询中的结果中包含null值,那么not in(null、xx、bb、cc)返回为空。

[oracle@rhel6_lhr ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.3.0 Production on Mon May 18 13:38:09 2015

Copyright (c) 1982, 2011, Oracle.  All rights reserved.

Connected to:

Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production

With the Partitioning, Automatic Storage Management, OLAP, Data Mining

and Real Application Testing options

13:38:09 SQL> drop table lhr.emp_bk;

Table dropped.

Elapsed: 00:00:04.16

13:38:15 SQL> create table lhr.emp_bk as select * from scott.emp;

Table created.

Elapsed: 00:00:00.77

13:41:01 SQL> create table lhr.dept_bk as select * from scott.dept;

Table created.

Elapsed: 00:00:00.13

13:41:43 SQL>  insert into lhr.dept_bk  values(50,'lhr','China');

1 row created.

Elapsed: 00:00:00.03

13:41:57 SQL> select * from lhr.dept_bk ;

    DEPTNO DNAME          LOC

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

        10 ACCOUNTING     NEW YORK

        20 RESEARCH       DALLAS

        30 SALES          CHICAGO

        40 OPERATIONS     BOSTON

        50 lhr            China

Elapsed: 00:00:00.01

13:42:48 SQL> select * from  lhr.emp_bk b;

     EMPNO ENAME      JOB              MGR HIREDATE                   SAL       COMM     DEPTNO

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

      7369 SMITH      CLERK           7902 1980-12-17 00:00:00      20800                    20

      7499 ALLEN      SALESMAN        7698 1981-02-20 00:00:00      31600        300         30

      7521 WARD       SALESMAN        7698 1981-02-22 00:00:00      31250        500         30

      7566 JONES      MANAGER         7839 1981-04-02 00:00:00      22975                    20

      7654 MARTIN     SALESMAN        7698 1981-09-28 00:00:00      31250       1400         30

      7698 BLAKE      MANAGER         7839 1981-05-01 00:00:00      32850                    30

      7782 CLARK      MANAGER         7839 1981-06-09 00:00:00      12450                    10

      7788 SCOTT      ANALYST         7566 1987-04-19 00:00:00      23000                    20

      7839 KING       PRESIDENT            1981-11-17 00:00:00      15000                    10

      7844 TURNER     SALESMAN        7698 1981-09-08 00:00:00      31500          0         30

      7876 ADAMS      CLERK           7788 1987-05-23 00:00:00      21100                    20

      7900 JAMES      CLERK           7698 1981-12-03 00:00:00      30950                    30

      7902 FORD       ANALYST         7566 1981-12-03 00:00:00      23000                    20

      7934 MILLER     CLERK           7782 1982-01-23 00:00:00      11300                    10

16 rows selected.

Elapsed: 00:00:00.02

13:44:00 SQL> select * from lhr.dept_bk a where  a.deptno not in(select b.deptno from lhr.emp_bk b);

    DEPTNO DNAME          LOC

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

        50 lhr            China

        40 OPERATIONS     BOSTON

Elapsed: 00:00:00.93

13:44:07 SQL> update lhr.emp_bk b set b.deptno=null where empno=7788;

1 row updated.

Elapsed: 00:00:00.04

13:45:17 SQL> select * from  lhr.emp_bk b;

     EMPNO ENAME      JOB              MGR HIREDATE                   SAL       COMM     DEPTNO

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

      7369 SMITH      CLERK           7902 1980-12-17 00:00:00      20800                    20

      7499 ALLEN      SALESMAN        7698 1981-02-20 00:00:00      31600        300         30

      7521 WARD       SALESMAN        7698 1981-02-22 00:00:00      31250        500         30

      7566 JONES      MANAGER         7839 1981-04-02 00:00:00      22975                    20

      7654 MARTIN     SALESMAN        7698 1981-09-28 00:00:00      31250       1400         30

      7698 BLAKE      MANAGER         7839 1981-05-01 00:00:00      32850                    30

      7782 CLARK      MANAGER         7839 1981-06-09 00:00:00      12450                    10

      7788 SCOTT      ANALYST         7566 1987-04-19 00:00:00      23000

      7839 KING       PRESIDENT            1981-11-17 00:00:00      15000                    10

      7844 TURNER     SALESMAN        7698 1981-09-08 00:00:00      31500          0         30

      7876 ADAMS      CLERK           7788 1987-05-23 00:00:00      21100                    20

      7900 JAMES      CLERK           7698 1981-12-03 00:00:00      30950                    30

      7902 FORD       ANALYST         7566 1981-12-03 00:00:00      23000                    20

      7934 MILLER     CLERK           7782 1982-01-23 00:00:00      11300                    10

14 rows selected.

Elapsed: 00:00:00.14

13:45:23 SQL> select * from lhr.dept_bk a where  a.deptno not in(select b.deptno from lhr.emp_bk b);

no rows selected

Elapsed: 00:00:00.00

13:45:39 SQL> select * from lhr.dept_bk a where  a.deptno not in(select b.deptno from lhr.emp_bk b where b.deptno is not null);

    DEPTNO DNAME          LOC

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

        50 lhr            China

        40 OPERATIONS     BOSTON

Elapsed: 00:00:00.04

13:46:01 SQL>

一.6.2 情形二:

要求返回所有比“ALLEN”提成低的员工:

14:01:07 SQL> select a.ename,a.comm from scott.emp a;

ENAME            COMM

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

SMITH

ALLEN             300

WARD              500

JONES

MARTIN           1400

BLAKE

CLARK

SCOTT

KING

TURNER              0

ADAMS

JAMES

FORD

MILLER

14 rows selected.

Elapsed: 00:00:00.23

14:01:17 SQL> select a.ename,a.comm from scott.emp a where a.comm < ( select b.comm from scott.emp b where b.ename='ALLEN');

ENAME            COMM

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

TURNER              0

Elapsed: 00:00:00.11

14:01:28 SQL> select a.ename,a.comm from scott.emp a where coalesce(a.comm,0) < ( select b.comm from scott.emp b where b.ename='ALLEN');

ENAME            COMM

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

SMITH

JONES

BLAKE

CLARK

SCOTT

KING

TURNER              0

ADAMS

JAMES

FORD

MILLER

11 rows selected.

Elapsed: 00:00:00.02

14:01:55 SQL>

一.7 总结

到此个人觉得本章的一些难点或需要补充的地方就这些了,希望大家看完有所收获。

一.8 about me

...........................................................................................................................................................................................

本文作者:小麦苗,只专注于数据库的技术,更注重技术的运用

ITPUB BLOG:http://blog.itpub.net/26736162

本文地址:http://blog.itpub.net/26736162/viewspace-1660422/

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创作时间地点:2015-05-15 10:00~ 2015-05-18 15:00 于×××交易中心

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