用法：

SELECT sys_context('USERENV', '') FROM dual;

第二個參數的可選值：

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_TYPE

How the user was authenticated:

DATABASE: username/passWord authentication

OS: Operating system external user authentication

NETWORK: network PRotocol or ANO authentication

PROXY: OCI proxy connection authentication

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_INFO

Returns up to 64 bytes of user session information that can be stored by an application using the DBMS_APPLICATION_INFO package.

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.

CURRENT_SCHEMAID

Identifier of the default schema being used in the current session.

CURRENT_USER

The name of the user whose privilege the current session is under.

CURRENT_USERID

User ID of the user whose privilege the current session is under.

DB_DOMAIN

Domain of the database as specified in the DB_DOMAIN initialization parameter.

DB_NAME

Name of the database as specified in the DB_NAME initialization parameter.

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.

EXTERNAL_NAME

External name of the database user. For SSL authenticated sessions using v.503 certificates, this field returns the distinguished name (DN) stored in the user certificate.

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.

HOST

Name of the host machine from which the client has connected.

INSTANCE

The instance identification number of the current instance.

ip_ADDRESS

IP address of the machine from which the client is connected.

ISDBA

TRUE if you are logged on as SYS.

LANG

The ISO abbreviation for the language name, a shorter form than the existing 'LANGUAGE' parameter.

LANGUAGE

The language and territory currently used by your session, along with the database character set, in the form:language_territory.characterset.

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.

NLS_CURRENCY

The currency of the current session.

NLS_DATE_FORMAT

The date format for the session.

NLS_DATE_LANGUAGE

The language used for expressing dates.

NLS_SORT BINARY

or the linguistic sort basis.

NLS_TERRITORY

The territory of the current session.

OS_USER

Operating system username of the client process that initiated the database session.

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.

SESSION_USER

Database user name by which the current user is authenticated. This value remains the same throughout the duration of the session.

SESSION_USERID

Identifier of the database user name by which the current user is authenticated.

SESSIONID

The auditing session identifier. You cannot use this option in distributed SQL statements.

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.)