说说sys_context函数

select SYS_CONTEXT('USERENV', 'TERMINAL') terminal,
       SYS_CONTEXT('USERENV', 'LANGUAGE') language,
       SYS_CONTEXT('USERENV', 'SESSIONID') sessionid,
       SYS_CONTEXT('USERENV', 'INSTANCE') instance,
       SYS_CONTEXT('USERENV', 'ENTRYID') entryid,
       SYS_CONTEXT('USERENV', 'ISDBA') isdba,
       SYS_CONTEXT('USERENV', 'NLS_TERRITORY') nls_territory,
       SYS_CONTEXT('USERENV', 'NLS_CURRENCY') nls_currency,
       SYS_CONTEXT('USERENV', 'NLS_CALENDAR') nls_calendar,
       SYS_CONTEXT('USERENV', 'NLS_DATE_FORMAT') nls_date_format,
       SYS_CONTEXT('USERENV', 'NLS_DATE_LANGUAGE') nls_date_language,
       SYS_CONTEXT('USERENV', 'NLS_SORT') nls_sort,
       SYS_CONTEXT('USERENV', 'CURRENT_USER') current_user,
       SYS_CONTEXT('USERENV', 'CURRENT_USERID') current_userid,
       SYS_CONTEXT('USERENV', 'SESSION_USER') session_user,
       SYS_CONTEXT('USERENV', 'SESSION_USERID') session_userid,
       SYS_CONTEXT('USERENV', 'PROXY_USER') proxy_user,
       SYS_CONTEXT('USERENV', 'PROXY_USERID') proxy_userid,
       SYS_CONTEXT('USERENV', 'DB_DOMAIN') db_domain,
       SYS_CONTEXT('USERENV', 'DB_NAME') db_name,
       SYS_CONTEXT('USERENV', 'HOST') host,
       SYS_CONTEXT('USERENV', 'OS_USER') os_user,
       SYS_CONTEXT('USERENV', 'EXTERNAL_NAME') external_name,
       SYS_CONTEXT('USERENV', 'IP_ADDRESS') ip_address,
       SYS_CONTEXT('USERENV', 'NETWORK_PROTOCOL') network_protocol,
       SYS_CONTEXT('USERENV', 'BG_JOB_ID') bg_job_id,
       SYS_CONTEXT('USERENV', 'FG_JOB_ID') fg_job_id,
       SYS_CONTEXT('USERENV', 'AUTHENTICATION_TYPE') authentication_type,
       SYS_CONTEXT('USERENV', 'AUTHENTICATION_DATA') authentication_data
  from dual

sys_context函数是Oracle提供的一个获取环境上下文信息的预定义函数。该函数用来返回一个指定namespace下的parameter值。该函数可以在SQL和PL/SQL语言中使用。

sys_context实际上就是一个Oracle
存储和传递参数的容器访问函数。我们登入Oracle服务器，是带有会话信息session_info和其他一些属性信息。其中，有一些是Oracle预
定义的，登录系统的时候自动填入到指定的变量中。还有一些是我们自己定义到其中，用于传递值使用的。

下面是sys_context函数的使用格式：

sys_context(‘namespace’,’parameter’{,length});

其中，namespace是存储信息的一个组
group单位，namespace是按照类别进行分类的。一个namespace下可以有多个参数值，通过不同的parameter进行区分。
namespace是预先定义好的SQL标识符，而parameter是可以任意大小写非敏感的字符串，不超过30位长度。

函数返回值为varchar2类型，长度默认为256位。如果需要限制这个默认值，可以数据length参数作为新的返回长度值。

设置namespace指定parameter值，可以使用dbms_session.set_context方法进行。

//自定义一个namespace，并且规定的设置的方法句柄；…………………….step 1

SQL> create context Test using set_test_context;

Context created

//定义方法…………………….step 2

create or replace procedure set_test_context

(

vc_value in varchar2

)

is

begin

dbms_session.set_context('Test','a1',vc_value);

end set_test_context;

//设置上值…………………….step 3

SQL> exec set_test_context('m');

PL/SQL procedure successfully completed

//获取这个值

SQL> select sys_context('Test','a1') from dual;

SYS_CONTEXT('TEST','A1')

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

m

step1-3很重要，因为Test namespace为自定义的namespace，所以需要这样的设置，以确定权限所属。

sys_context函数最常用的就是userenv命名空间下的系列参数。下面是参数列表，摘自

http://hi.baidu.com/edeed/blog/item/28cba0ecaa6c8e3e269791bb.html；

Attribute	Return Value
ACTION	Identifies the position in the module (application name) and is set through the DBMS_APPLICATION_INFO package or OCI.
	SELECTsys_context('USERENV', 'ACTION') FROM dual; exec dbms_application_info.set_action('INSERTING'); SELECTsys_context('USERENV', 'ACTION') FROM dual;
AUDITED_CURSORID	Returns the cursor ID of the SQL that triggered the audit. This parameter is not valid in a fine-grained auditing environment. If you specify it in such an environment, Oracle Database always returns NULL.
AUTHENTICATED_IDENTITY	Returns the identity used in authentication. In the list that follows, the type of user is followed by the value returned: Kerberos-authenticated enterprise user: kerberos principal name Kerberos-authenticated external user : kerberos principal name; same as the schema name SSL-authenticated enterprise user: the DN in the user's PKI certificate SSL-authenticated external user: the DN in the user's PKI certificate Password-authenticated enterprise user: nickname; same as the login name Password-authenticated database user: the database username; same as the schema name OS-authenticated external user: the external operating system user name Radius/DCE-authenticated external user: the schema name Proxy with DN : Oracle Internet Directory DN of the client Proxy with certificate: certificate DN of the client Proxy with username: database user name if client is a local database user; nickname if client is an enterprise user SYSDBA/SYSOPER using Password File: login name SYSDBA/SYSOPER using OS authentication: operating system user name
AUTHENTICATION_DATA	Data being used to authenticate the login user. For X.503 certificate authenticated sessions, this field returns the context of the certificate in HEX2 format. Note:You can change the return value of the AUTHENTICATION_DATA attribute using the length parameter of the syntax. Values of up to 4000 are accepted. This is the only attribute of USERENV for which Oracle implements such a change.
AUTHENTICATION_METHOD	Returns the method of authentication. In the list that follows, the type of user is followed by the method returned. Password-authenticated enterprise user, local database user, or SYSDBA/SYSOPER using Password File; proxy with username using password: PASSWORD Kerberos-authenticated enterprise or external user: KERBEROS SSL-authenticated enterprise or external user: SSL Radius-authenticated external user: RADIUS OS-authenticated external user or SYSDBA/SYSOPER: OS DCE-authenticated external user: DCE Proxy with certificate, DN, or username without using password: NONE
BG_JOB_ID	Job ID of the current session if it was established by an Oracle background process. Null if the session was not established by a background process.
CLIENT_IDENTIFIER	Returns an identifier that is set by the application through the DBMS_SESSION.SET_IDENTIFIER procedure, the OCI attribute OCI_ATTR_CLIENT_IDENTIFIER, or the Java class Oracle.jdbc.OracleConnection.setClientIdentifier. This attribute is used by various database components to identify lightweight application users who authenticate as the same user.
	SELECTsys_context('USERENV', 'CLIENT_IDENTIFIER') FROM dual; exec dbms_session.set_identifier(USER || ' ' || SYSTIMESTAMP); SELECTsys_context('USERENV', 'CLIENT_IDENTIFIER') FROM dual;
CLIENT_INFO	Returns user session information that can be stored by an application using the DBMS_APPLICATION_INFO package.
	SELECTsys_context('USERENV', 'CLIENT_INFO') FROM dual; exec dbms_application_info.set_client_info('TEST'); SELECTsys_context('USERENV', 'CLIENT_INFO') FROM dual;
CURRENT_BIND	The bind variables for fine-grained auditing
CURRENT_EDITION_ID	The name of the current edition
	SELECTsys_context('USERENV', 'CURRENT_EDITION_ID') FROM dual;
CURRENT_EDITION_NAME	The name of the current edition
	SELECTsys_context('USERENV', 'CURRENT_EDITION_NAME') FROM dual;
CURRENT_SCHEMA	Name of the default schema being used in the current schema. This value can be changed during the session with an ALTER SESSION SET CURRENT_SCHEMA statement.
	SELECTsys_context('USERENV', 'CURRENT_SCHEMA') FROM dual;
CURRENT_SCHEMAID	Identifier of the default schema being used in the current session.
	SELECTsys_context('USERENV', 'CURRENT_SCHEMAID') FROM dual; SELECT user# FROM sys.user$ WHERE name = USER;
CURRENT_SQL	Returns the first 4K bytes of the current SQL that triggered the fine-grained auditing event.
CURRENT_SQLn	CURRENT_SQLnattributes return subsequent 4K-byte increments, where n can be an integer from 1 to 7, inclusive. CURRENT_SQL1 returns bytes 4K to 8K; CURRENT_SQL2 returns bytes 8K to 12K, and so forth. You can specify these attributes only inside the event handler for the fine-grained auditing feature.
CURRENT_SQL_LENGTH	The length of the current SQL statement that triggers fine-grained audit or row-level security (RLS) policy functions or event handlers. Valid only inside the function or event handler.
DB_DOMAIN	Domain of the database as specified in the DB_DOMAIN initialization parameter.
	SELECTsys_context('USERENV', 'DB_DOMAIN') FROM dual;
DB_NAME	Name of the database as specified in the DB_NAME initialization parameter.
	SELECTsys_context('USERENV', 'DB_NAME') FROM dual; SELECT name, value FROM gv$parameter where name LIKE 'db%name';
DB_UNIQUE NAME	Name of the database as specified in the DB_UNIQUE_NAME initialization parameter.
	SELECTsys_context('USERENV', 'DB_UNIQUE_NAME') FROM dual; SELECT name, value FROM gv$parameter where name LIKE 'db%name';
ENTRYID	The available auditing entry identifier. You cannot use this option in distributed SQL statements. To use this keyword in USERENV, the initialization parameter AUDIT_TRAIL must be set to true.
ENTERPRISE_IDENTITY	Returns the user's enterprise-wide identity: For enterprise users: the Oracle Internet Directory DN. For external users: the external identity (Kerberos principal name, Radius and DCE schema names, OS user name, Certificate DN). For local users and SYSDBA/SYSOPER logins: NULL. The value of the attribute differs by proxy method: For a proxy with DN: the Oracle Internet Directory DN of the client For a proxy with certificate: the certificate DN of the client for external users; the Oracle Internet Directory DN for global users For a proxy with username: the Oracle Internet Directory DN if the client is an enterprise users; NULL if the client is a local database user.
FG_JOB_ID	Job ID of the current session if it was established by a client foreground process. Null if the session was not established by a foreground process.
GLOBAL_CONTEXT_MEMORY	The number used in the System Global Area by the globally accessed context.
	SELECTsys_context('USERENV', 'GLOBAL_CONTEXT_MEMORY') FROM dual;
GLOBAL_UID	Returns the global user ID from Oracle Internet Directory for Enterprise User Security (EUS) logins; returns null for all other logins.
HOST	Name of the host machine from which the client has connected.
	SELECTsys_context('USERENV', 'HOST') FROM dual;
IDENTIFICATION_TYPE	Returns the way the user's schema was created in the database. Specifically, it reflects the IDENTIFIED clause in the CREATE/ALTER USER syntax. In the list that follows, the syntax used during schema creation is followed by the identification type returned: IDENTIFIED BY password: LOCAL IDENTIFIED EXTERNALLY: EXTERNAL IDENTIFIED GLOBALLY: GLOBAL SHARED IDENTIFIED GLOBALLY AS DN: GLOBAL PRIVATE
	SELECTsys_context('USERENV', 'IDENTIFICATION_TYPE') FROM dual;
INSTANCE	The instance identification number of the current instance.
	SELECTsys_context('USERENV', 'INSTANCE') FROM dual;
INSTANCE_NAME	The name of the instance.
	SELECTsys_context('USERENV', 'INSTANCE_NAME') FROM dual;
IP_ADDRESS	IP address of the machine from which the client is connected.
ISDBA	TRUE if the session is SYS
	SELECTsys_context('USERENV', 'ISDBA') FROM dual;
LANG	The ISO abbreviation for the language name, a shorter form. than the existing 'LANGUAGE' parameter.
	SELECTsys_context('USERENV', 'LANG') FROM dual;
LANGUAGE	The language and territory currently used by your session, along with the database character set, in the form.: language_territory.characterset.
	SELECTsys_context('USERENV', 'LANGUAGE') FROM dual;
MODULE	The application name (module) set through the DBMS_APPLICATION_INFO package or OCI.
	SELECTsys_context('USERENV', 'MODULE') FROM dual;
NETWORK_PROTOCOL	Network protocol being used for communication, as specified in the 'PROTOCOL=protocol' portion of the connect string.
NLS_CALENDAR	The current calendar of the current session.
	SELECTsys_context('USERENV', 'NLS_CALENDAR') FROM dual;
NLS_CURRENCY	The currency of the current session.
	SELECTsys_context('USERENV', 'NLS_CURRENCY') FROM dual;
NLS_DATE_FORMAT	The date format for the session.
	SELECTsys_context('USERENV', 'NLS_DATE_FORMAT') FROM dual;
NLS_DATE_LANGUAGE	The language used for expressing dates.
	SELECTsys_context('USERENV', 'NLS_DATE_LANGUAGE') FROM dual;
NLS_SORT	BINARY or the linguistic sort basis.
	SELECTsys_context('USERENV', 'NLS_SORT') FROM dual;
NLS_TERRITORY	The territory of the current session.
	SELECTsys_context('USERENV', 'NLS_TERRITORY') FROM dual;
OS_USER	Operating system username of the client process that initiated the database session.
	SELECTsys_context('USERENV', 'OS_USER') FROM dual;
POLICY_INVOKER	The invoker of row-level security (RLS) policy functions.
PROXY_ENTERPRISE_IDENTITY	Returns the Oracle Internet Directory DN when the proxy user is an enterprise user.
PROXY_GLOBAL_UID	Returns the global user ID from Oracle Internet Directory for Enterprise User Security (EUS) proxy users; returns NULL for all other proxy users.
PROXY_USER	Name of the database user who opened the current session on behalf of SESSION_USER.
PROXY_USERID	Identifier of the database user who opened the current session on behalf of SESSION_USER.
SERVER_HOST	The host name of the machine on which the instance is running.
	SELECTsys_context('USERENV', 'SERVER_HOST') FROM dual;
SERVICE_NAME	The name of the service to which a given session is connected.
	SELECTsys_context('USERENV', 'SERVICE_NAME') FROM dual;
SESSION_USER	Database user name by which the current user is authenticated. This value remains the same throughout the duration of the session.
	SELECTsys_context('USERENV', 'SESSION_USER') FROM dual;
SESSION_USERID	Identifier of the database user name by which the current user is authenticated.
	SELECTsys_context('USERENV', 'SESSION_USERID') FROM dual;
SESSIONID	The auditing session identifier. You cannot use this option in distributed SQL statements. This is the equivalent to the AUDSID column ingv$session.
	SELECTsys_context('USERENV', 'SESSIONID') FROM dual;
SID	The session number (different from the session ID).
	SELECTsys_context('USERENV', 'SID') FROM dual;
STATEMENTID	The auditing statement identifier. STATEMENTID represents the number of SQL statements audited in a given session.
TERMINAL	The operating system identifier for the client of the current session. In distributed SQL statements, this option returns the identifier for your local session. In a distributed environment, this is supported only for remote SELECT statements, not for remote INSERT, UPDATE, or DELETE operations. (The return length of this parameter may vary by operating system.)
	SELECTsys_context('USERENV', 'TERMINAL') FROM dual;

例子：

SQL> select sys_context('userenv','ip_address') from dual;

SYS_CONTEXT('USERENV','IP_ADDR

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

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