sys_context - Obtener información de la sesión

sys_context( namespace, parameter, [ length ] )

Surgió la necesidad de obtener el usuario del S.O. con el que estaba
logeado el usuario que había iniciado la sesión de Oracle, y lo obtuvimos así:

Para obtener el usuario del S.O:

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

Otros ejemplos:

Para obtener el nombre de la base de datos:
SELECT sys_context('USERENV', 'DB_NAME') FROM dual

Para obtener el eschema actual de la base de datos:
SELECT sys_context('USERENV', 'CURRENT_SCHEMA') FROM dual


Existen muchos otros parámetros.

Dejo este enlace
http://www.techonthenet.com/oracle/functions/sys_context.php

Los parametros posibles para el namespace 'USERENV' son estos:

• AUDITED_CURSORID: Returns the cursor ID of the SQL that triggered the audit
• AUTHENTICATION_DATA: Authentication data
• AUTHENTICATION_TYPE: Describes how the user was authenticated. Can be one of the following values: Database, OS, Network, or Proxy
• BG_JOB_ID: If the session was established by an Oracle background process, this parameter will return the Job ID. Otherwise, it will return NULL.
• CLIENT_IDENTIFIER: Returns the client identifier (global context)
• CLIENT_INFO: User session information
• CURRENT_SCHEMA: Returns the default schema used in the current schema
• CURRENT_SCHEMAID: Returns the identifier of the default schema used in the current schema
• CURRENT_SQL: Returns the SQL that triggered the audit event
• CURRENT_USER: Name of the current user
• CURRENT_USERID: Userid of the current user
• DB_DOMAIN: Domain of the database from the DB_DOMAIN initialization parameter
• DB_NAME: Name of the database from the DB_NAME initialization parameter
• ENTRYID: Available auditing entry identifier
• EXTERNAL_NAME: External of the database user
• FG_JOB_ID: If the session was established by a client foreground process, this parameter will return the Job ID. Otherwise, it will return NULL.
• GLOBAL_CONTEXT_MEMORY: The number used in the System Global Area by the globally accessed context
• HOST:nName of the host machine from which the client has connected
• INSTANCE: The identifier number of the current instance
• IP_ADDRESS: IP address of the machine from which the client has connected
• ISDBA: Returns TRUE if the user has DBA privileges. Otherwise, it will return FALSE.
• LANG: The ISO abbreviate for the language
• LANGUAGE: The language, territory, and character of the session. In the following format: language_territory.characterset
• NETWORK_PROTOCOL: Network protocol used
• NLS_CALENDAR: The calendar of the current session
• NLS_CURRENCY: The currency of the current session
• NLS_DATE_FORMAT: The date format for the current session
• NLS_DATE_LANGUAGE: The language used for dates
• NLS_SORT: BINARY or the linguistic sort basis
• NLS_TERRITORY: The territory of the current session
• OS_USER: The OS username for the user logged in
• PROXY_USER: The name of the user who opened the current session on behalf of SESSION_USER
• PROXY_USERID: The identifier of the user who opened the current session on behalf of SESSION_USER
• SESSION_USER: The database user name of the user logged in
• SESSION_USERID: The database identifier of the user logged in
• SESSIONID: The identifier of the auditing session
• TERMINAL: The OS identifier of the current session