【书评:Oracle查询优化改写】第三章

【书评:Oracle查询优化改写】第三章 BLOG文档结构图    


 

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oracle9i之前默认值为true。可以这样认为，如有两个字段B都有oracle有可能将这两个索引转换成and操作得出结果集。如果改为btree的索引，我们可以将该参数在false，也可以加Oracle也可以将数据记录的_b_tree_bitmap_plans设置为”（“或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，false后，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：   [b]http://blog.itpub.net/26736162/viewspace-1660038/   我们在http://blog.itpub.net/26736162/viewspace-1652985/）中总结了一下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“