①创建表t
SQL> create table t as select * from dba_objects;

Table created.

--收集直方图

SQL> exec dbms_stats.gather_table_stats(user,'T');

PL/SQL procedure successfully completed.

--此时数据库为表上的所有字段收集了缺省的统计信息，每个列两个Bucket：

SQL> col column_name for a30

SQL> col owner for a10

SQL> col table_name for a10

SQL> col ENDPOINT_ACTUAL_VALUE for a10

②查询

SQL> select * from dba_tab_histograms where table_name='T' and owner='SYS' order by 3;

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T CREATED 1

2457673.05

SYS T CREATED 0

2456529.48

SYS T DATA_OBJECT_ID 1

88710

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T DATA_OBJECT_ID 0

0

SYS T GENERATED 0

4.0500E+35

SYS T GENERATED 1

4.6211E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T LAST_DDL_TIME 1

2457673.05

SYS T LAST_DDL_TIME 0

2452549.53

SYS T NAMESPACE 0

1

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T NAMESPACE 1

64

SYS T OBJECT_ID 1

88710

SYS T OBJECT_ID 0

2

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T OBJECT_NAME 0

2.4504E+35

SYS T OBJECT_NAME 1

6.2963E+35

SYS T OBJECT_TYPE 0

3.4943E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T OBJECT_TYPE 1

4.5849E+35

SYS T OWNER 0

3.3913E+35

SYS T OWNER 1

4.5831E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T SECONDARY 1

4.6211E+35

SYS T SECONDARY 0

4.0500E+35

SYS T STATUS 1

4.4786E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T STATUS 0

4.4786E+35

SYS T SUBOBJECT_NAME 1

4.5340E+35

SYS T SUBOBJECT_NAME 0

1.8867E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T TEMPORARY 1

4.6211E+35

SYS T TEMPORARY 0

4.0500E+35

SYS T TIMESTAMP 0

2.5558E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T TIMESTAMP 1

2.6059E+35
28 rows selected.
--同时，列的低值、高值等信息会被收集记录在dba_tab_col_statistics中：
SQL> select table_name,column_name,num_distinct,low_value,high_value,DENSITY from dba_tab_col_statistics where owner='SYS' and table_name='T';

TABLE_NAME COLUMN_NAME NUM_DISTINCT

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

LOW_VALUE

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

HIGH_VALUE DENSITY

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

T OWNER 29

415045585F303330323030

584442 .034482759

T OBJECT_NAME 52212

2F31303030333233645F44656C6567617465496E766F636174696F6E4861

794362437253756253616D706C696E67547970653232395F54 .000019153

TABLE_NAME COLUMN_NAME NUM_DISTINCT

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

LOW_VALUE

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

HIGH_VALUE DENSITY

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

T SUBOBJECT_NAME 150

2456534E5F31

575248245F5741495453545F3234313436323135355F30 .006666667

T OBJECT_ID 86995

C103

TABLE_NAME COLUMN_NAME NUM_DISTINCT

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

LOW_VALUE

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

HIGH_VALUE DENSITY

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

C309580B .000011495

T DATA_OBJECT_ID 9106

80

C309580B .000109818

T OBJECT_TYPE 45

TABLE_NAME COLUMN_NAME NUM_DISTINCT

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

LOW_VALUE

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

HIGH_VALUE DENSITY

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

434C5553544552

584D4C20534348454D41 .022222222

T CREATED 978

787108180C2624

78740A0B02082A .001022495

TABLE_NAME COLUMN_NAME NUM_DISTINCT

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

LOW_VALUE

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

HIGH_VALUE DENSITY

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

T LAST_DDL_TIME 1096

78660A010D2A32

78740A0B02082A .000912409

T TIMESTAMP 1130

313939302D30382D32363A31313A32353A3030

323031362D31302D31313A30313A30373A3431 .000884956

TABLE_NAME COLUMN_NAME NUM_DISTINCT

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

LOW_VALUE

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

HIGH_VALUE DENSITY

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

T STATUS 1

56414C4944

56414C4944 1

T TEMPORARY 2

4E

TABLE_NAME COLUMN_NAME NUM_DISTINCT

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

LOW_VALUE

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

HIGH_VALUE DENSITY

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

59 .5

T GENERATED 2

4E

59 .5

T SECONDARY 2

TABLE_NAME COLUMN_NAME NUM_DISTINCT

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

LOW_VALUE

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

HIGH_VALUE DENSITY

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

4E

59 .5

T NAMESPACE 21

C102

C141 .047619048

TABLE_NAME COLUMN_NAME NUM_DISTINCT

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

LOW_VALUE

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

HIGH_VALUE DENSITY

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

T EDITION_NAME 0

0

15 rows selected.

③SQL> exec dbms_stats.gather_table_stats(user,'T',method_opt=> 'for all columns size 1');

PL/SQL procedure successfully completed.

SQL> exec dbms_stats.gather_table_stats(user,'T',method_opt=>'for columns owner size 1');

PL/SQL procedure successfully completed.
或删除owner字段统计信息，（无用）

--查询发现直方图信息并未被删除
SQL> select * from dba_tab_histograms where table_name='T' and owner='SYS' order by 3;

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T CREATED 1

2457673.05

SYS T CREATED 0

2456529.48

SYS T DATA_OBJECT_ID 1

88710

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T DATA_OBJECT_ID 0

0

SYS T GENERATED 0

4.0500E+35

SYS T GENERATED 1

4.6211E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T LAST_DDL_TIME 1

2457673.05

SYS T LAST_DDL_TIME 0

2452549.53

SYS T NAMESPACE 0

1

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T NAMESPACE 1

64

SYS T OBJECT_ID 1

88710

SYS T OBJECT_ID 0

2

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T OBJECT_NAME 0

2.4504E+35

SYS T OBJECT_NAME 1

6.2963E+35

SYS T OBJECT_TYPE 0

3.4943E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T OBJECT_TYPE 1

4.5849E+35

SYS T OWNER 0

3.3913E+35

SYS T OWNER 1

4.5831E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T SECONDARY 1

4.6211E+35

SYS T SECONDARY 0

4.0500E+35

SYS T STATUS 1

4.4786E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T STATUS 0

4.4786E+35

SYS T SUBOBJECT_NAME 1

4.5340E+35

SYS T SUBOBJECT_NAME 0

1.8867E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T TEMPORARY 1

4.6211E+35

SYS T TEMPORARY 0

4.0500E+35

SYS T TIMESTAMP 0

2.5558E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T TIMESTAMP 1

2.6059E+35

28 rows selected.

④使用delete_column_stats可以彻底删除列的柱状图信息：

SQL> exec dbms_stats.delete_column_stats(user,'T','OWNER');

PL/SQL procedure successfully completed.

--此时查询发现owner字段在直方图中已经删除

SQL> select * from dba_tab_histograms where table_name='T' and owner='SYS' order by 3;

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T CREATED 1

2457673.05

SYS T CREATED 0

2456529.48

SYS T DATA_OBJECT_ID 1

88710

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T DATA_OBJECT_ID 0

0

SYS T GENERATED 0

4.0500E+35

SYS T GENERATED 1

4.6211E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T LAST_DDL_TIME 1

2457673.05

SYS T LAST_DDL_TIME 0

2452549.53

SYS T NAMESPACE 1

64

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T NAMESPACE 0

1

SYS T OBJECT_ID 1

88710

SYS T OBJECT_ID 0

2

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T OBJECT_NAME 0

2.4504E+35

SYS T OBJECT_NAME 1

6.2963E+35

SYS T OBJECT_TYPE 1

4.5849E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T OBJECT_TYPE 0

3.4943E+35

SYS T SECONDARY 0

4.0500E+35

SYS T SECONDARY 1

4.6211E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T STATUS 0

4.4786E+35

SYS T STATUS 1

4.4786E+35

SYS T SUBOBJECT_NAME 0

1.8867E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T SUBOBJECT_NAME 1

4.5340E+35

SYS T TEMPORARY 0

4.0500E+35

SYS T TEMPORARY 1

4.6211E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T TIMESTAMP 1

2.6059E+35

SYS T TIMESTAMP 0

2.5558E+35

26 rows selected.

⑤再次收集，owner字段又回来了

SQL> exec dbms_stats.gather_table_stats(user,'T');

PL/SQL procedure successfully completed.

SQL> select * from dba_tab_histograms where table_name='T' and owner='SYS' order by 3;

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T CREATED 1

2457673.05

SYS T CREATED 0

2456529.48

SYS T DATA_OBJECT_ID 1

88710

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T DATA_OBJECT_ID 0

0

SYS T GENERATED 0

4.0500E+35

SYS T GENERATED 1

4.6211E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T LAST_DDL_TIME 1

2457673.05

SYS T LAST_DDL_TIME 0

2452549.53

SYS T NAMESPACE 0

1

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T NAMESPACE 1

64

SYS T OBJECT_ID 1

88710

SYS T OBJECT_ID 0

2

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T OBJECT_NAME 0

2.4504E+35

SYS T OBJECT_NAME 1

6.2963E+35

SYS T OBJECT_TYPE 0

3.4943E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T OBJECT_TYPE 1

4.5849E+35

SYS T OWNER 0

3.3913E+35

SYS T OWNER 1

4.5831E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T SECONDARY 1

4.6211E+35

SYS T SECONDARY 0

4.0500E+35

SYS T STATUS 1

4.4786E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T STATUS 0

4.4786E+35

SYS T SUBOBJECT_NAME 1

4.5340E+35

SYS T SUBOBJECT_NAME 0

1.8867E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T TEMPORARY 1

4.6211E+35

SYS T TEMPORARY 0

4.0500E+35

SYS T TIMESTAMP 0

2.5558E+35

OWNER TABLE_NAME COLUMN_NAME ENDPOINT_NUMBER

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

ENDPOINT_VALUE ENDPOINT_A

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

SYS T TIMESTAMP 1

2.6059E+35

28 rows selected.

SQL> exec dbms_stats.gather_table_stats(user,'T',method_opt=>'for columns owner size 1');

PL/SQL procedure successfully completed.

【练习】ORACLE统计信息--直方图的更多相关文章

  1. 有关Oracle统计信息的知识点[z]

    https://www.cnblogs.com/sunmengbbm/p/5775211.html 一.什么是统计信息 统计信息主要是描述数据库中表,索引的大小,规模,数据分布状况等的一类信息.例如, ...

  2. 有关Oracle统计信息的知识点

    一.什么是统计信息 统计信息主要是描述数据库中表,索引的大小,规模,数据分布状况等的一类信息.例如,表的行数,块数,平均每行的大小,索引的leaf blocks,索引字段的行数,不同值的大小等,都属于 ...

  3. SQL Server 中统计信息直方图中对于没有覆盖到谓词预估以及预估策略的变化（SQL2012-->SQL2014-->SQL2016）

    本位出处:http://www.cnblogs.com/wy123/p/6770258.html 统计信息写过几篇了相关的文章了,感觉还是不过瘾,关于统计信息的问题,最近又踩坑了,该问题虽然不算很常见 ...

  4. MySQL 8.0 中统计信息直方图的尝试

    直方图是表上某个字段在按照一定百分比和规律采样后的数据分布的一种描述,最重要的作用之一就是根据查询条件,预估符合条件的数据量,为sql执行计划的生成提供重要的依据在MySQL 8.0之前的版本中,My ...

  5. [Oracle] oracle统计信息

    Oracle统计信息 Oracle数据库里的统计信息可以分为6种类型: 表的统计信息 索引的统计信息 列的统计信息 系统统计信息 数据字典统计信息 内部对象统计信息 图 1: Oracle统计信息 基 ...

  6. oracle统计信息

    手工刷ORACLE统计信息  select count(1) from LOG_TRX_DETAIL;  select * from user_tab_statistics where table_n ...

  7. 收集oracle统计信息

    优化器统计范围: 表统计: --行数,块数,行平均长度:all_tables:NUM_ROWS,BLOCKS,AVG_ROW_LEN:列统计: --列中唯一值的数量(NDV),NULL值的数量,数据分 ...

  8. Oracle 统计信息收集

    官网网址参考: https://docs.oracle.com/cd/B19306_01/appdev.102/b14258/d_stats.htm#CIHBIEII https://docs.ora ...

  9. 测试Oracle统计信息的导出导入

    背景:有时我们会希望可以对Oracle的统计信息整体进行导出导入.比如在数据库迁移前后,希望统计信息保持不变;又比如想对统计信息重新进行收集,但是担心重新收集的结果反而引发性能问题,想先保存当前的统计 ...

随机推荐

  1. MySQL存储引擎【InnoDB、MyISAM、Memory】

    数据库,MySQL这样存在多存储引擎的数据库软件,清楚常见的存储引擎的区别,使用合适的存储引擎,使得项目跑的更顺畅,有时候对于一个项目,甚至比项目本身都重要.这篇文章,旨在浅谈常见的三种存储引擎的区别 ...

  2. vim制作c的IDE

    编译vim源码 (1)安装依赖 sudo apt-get install python-dev python3-dev ruby-dev libx11-dev libgtk2.0-dev libgtk ...

  3. (VS TFS) Adding existing project to solution in TFS.

    正常的情况话,直接加入project,然后选择"Source control" -> “Add selected projects to source control.... ...

  4. jQuery插件：用于获取元素自身的HTML内容

    jQuery.fn.outerHTML = function(s) { return (s) ? this.before(s).remove() : $("<Hill_man>& ...

  5. [MySQL] 两个优化数据库表的简单方法--18.3

    这里介绍两个简单的优化MySQL数据库表的方法 一.定期分析表和检查表 1.分析表语法如下: alalyze [local|no_write_to_binlog] table table_name1[ ...

  6. php 信号量

    一些理论基础: 信号量:又称为信号灯.旗语 用来解决进程(线程同步的问题),类似于一把锁,访问前获取锁(获取不到则等待),访问后释放锁. 临界资源:每次仅允许一个进程访问的资源. 临界区:每个进程中访 ...

  7. 转-封装网络请求库，统一处理通用异常 (基于volley网络请求库)

    http://blog.csdn.net/kroclin/article/details/40540761 一.前言 volley的发布让网络请求也变得十分便利,但是我们通常懒得很想用一两句代码实现一 ...

  8. 火狐firefox提示“内容编码错误 无法显示您尝试查看的页面，因为它使用了无效或者不支持的压缩格式。”

    火狐firefox浏览器打开网也是时提示“内容编码错误 无法显示您尝试查看的页面,因为它使用了无效或者不支持的压缩格式.” 今早一来打开用PHPCMS做的网站时就提示这个错误,用其他浏览器打开提示的是 ...

  9. 为什么选择 Yeoman 及 Yeoman 的安装

    今天向您介绍一个我刚接触到的比较新的网络前端开发工具: Yeoman . 什么是Yeoman? Yeoman是Google的团队和外部贡献者团队合作开发的一个项目.通过内部三个工具(yo,grunt, ...

  10. 20145305 《Java程序设计》第6周学习总结

    教材学习内容总结 1.输入串流代表对象为java.io.InputStream实例,输出串流代表对象为java.io.OutputStream实例 2.InputStream与OutputStream ...