[20171115]关于namespace.txt
--//第一次听到这个概念,好像是那篇blog提到,表与索引在不同的namespace里面.也就是在相同schema下建立的表可以与索引同名.
--//而在同一schema下的namespace的建立的对象名字是不能重名的.
--//前几天在测试dbms_shared_pool.pin时,发现SEQUENCE的namespace竟然是TABLE/PROCEDURE,感觉有必要做一些学习,了解这方面
--//的知识.
--//摘要: http://blog.csdn.net/tianlesoftware/article/details/6624122
Oracle通过namespace来管理schema object的名字，关于Namespace 的定义，在官网文档上没有找到一个详细的定义，在网上搜到一些相
关信息：
Schema Object Namespaces
A namespace defines a group of object types, within which all names must be uniquely identified—by schema and name.
Objects in different namespaces can share the same name.
The Oracle database uses namespaces to resolve schema object references. When you refer to an object in a SQL statement,
Oracle considers the context of the SQL statement and locates the object in the appropriate namespace. After locating
the object, Oracle performs the operation specified by the statement on the object. If the named object cannot be found
in the appropriate namespace,then Oracle returns an error.
Because tables and views are in the same namespace, a table and a view in the same schema cannot have the same name.
However, tables and indexesare in different namespaces. Therefore, a table and an index in the same schemacan have the
same name.
Eachschema in the database has its own namespaces for the objects it contains. This means, for example, that two tables
in different schemas are in different namespaces and can have the same name.
--以上解释提到了几点：
1.每个用户都有自己对应的namespace来保存自己的对象
2.表和视图存放在同一个namespace,所以对于同一个用户的表和视图不能重名,但是表和索引是存放在不同的namespace，所以可以重名。
1.环境:
SCOTT@book> @ &r/ver1
PORT_STRING VERSION BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx 11.2.0.4.0 Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
2.测试:
SYS@book> select distinct kglhdnsp,kglhdnsd,kglobtyd from x$kglob order by 1;
KGLHDNSP KGLHDNSD KGLOBTYD
-------- ------------------------------- ---------------------------------
0 SQL AREA CURSOR
1 TABLE/PROCEDURE CURSOR
1 TABLE/PROCEDURE FUNCTION
1 TABLE/PROCEDURE LIBRARY
1 TABLE/PROCEDURE OPERATOR
1 TABLE/PROCEDURE PACKAGE
1 TABLE/PROCEDURE PROCEDURE
1 TABLE/PROCEDURE SEQUENCE
1 TABLE/PROCEDURE SYNONYM
1 TABLE/PROCEDURE TABLE
1 TABLE/PROCEDURE TYPE
1 TABLE/PROCEDURE VIEW
2 BODY CURSOR
2 BODY PACKAGE BODY
2 BODY TYPE BODY
4 INDEX INDEX
5 CLUSTER CLUSTER
10 QUEUE QUEUE
18 PUB SUB INTERNAL INFORMATION PUB SUB INTERNAL INFORMATION
23 RULESET RULESET
24 RESOURCE MANAGER RESOURCE MANAGER CONSUMER GROUP
45 MULTI-VERSION OBJECT FOR TABLE MULTI-VERSIONED OBJECT
48 MULTI-VERSION OBJECT FOR INDEX MULTI-VERSIONED OBJECT
51 SCHEDULER GLOBAL ATTRIBUTE CURSOR
51 SCHEDULER GLOBAL ATTRIBUTE SCHEDULER GLOBAL ATTRIBUTE
52 SCHEDULER EARLIEST START TIME SCHEDULER EARLIEST START TIME
64 EDITION EDITION
69 DBLINK CURSOR
73 SCHEMA CURSOR
73 SCHEMA NONE
74 DBINSTANCE CURSOR
75 SQL AREA STATS CURSOR STATS
79 ACCOUNT_STATUS NONE
82 SQL AREA BUILD CURSOR
34 rows selected.
--//个人感觉查询比较全,至少我机器正在运行的namespace.
https://docs.oracle.com/cd/B28359_01/server.111/b28286/sql_elements008.htm#SQLRF51109
Within a namespace, no two objects can have the same name.
The following schema objects share one namespace:
Tables
Views
Sequences
Private synonyms
Stand-alone procedures
Stand-alone stored functions
Packages
Materialized views
User-defined types
Each of the following schema objects has its own namespace:
Indexes
Constraints
Clusters
Database triggers
Private database links
Dimensions
Because tables and views are in the same namespace, a table and a view in the same schema cannot have the same name.
However, tables and indexes are in different namespaces. Therefore, a table and an index in the same schema can have the
same name.
Each schema in the database has its own namespaces for the objects it contains. This means, for example, that two tables
in different schemas are in different namespaces and can have the same name.
Each of the following nonschema objects also has its own namespace:
User roles
Public synonyms
Public database links
Tablespaces
Profiles
Parameter files (PFILEs) and server parameter files (SPFILEs)
Because the objects in these namespaces are not contained in schemas, these namespaces span the entire database.
--//注意看同义词,Private synonyms与table在一个名字空间里面,而 Public synonyms是分开单独的名字空间.
--//这些概念不小心还是乱...
--//继续做一些测试:
1.环境:
SCOTT@book> @ &r/ver1
PORT_STRING VERSION BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx 11.2.0.4.0 Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
2.测试:
SCOTT@book> CREATE SYNONYM DEPT FOR SCOTT.DEPT;
CREATE SYNONYM DEPT FOR SCOTT.DEPT
*
ERROR at line 1:
ORA-01471: cannot create a synonym with same name as object
--//而建立PUBLIC SYNONYM 就没有问题.
SCOTT@book> CREATE PUBLIC SYNONYM DEPT FOR SCOTT.DEPT;
Synonym created.
SCOTT@book> drop PUBLIC SYNONYM DEPT ;
Synonym dropped.
--//因为这两者属于不同的名字空间,这就很好理解.