Active parameters
ACTION, AUDITED_CURSORID, AUTHENTICATED_IDENTITY, AUTHENTICATION_DATA, AUTHENTICATION_METHOD, BG_JOB_ID, CLIENT_IDENTIFIER, CLIENT_INFO, CURRENT_BIND, CURRENT_SCHEMA, CURRENT_SCHEMAID, CURRENT_SQL, CURRENT_SQLn, CURRENT_SQL_LENGTH, DB_DOMAIN, DB_NAME, DB_UNIQUE_NAME, ENTRYID, ENTERPRISE_IDENTITY, FG_JOB_ID, GLOBAL_CONTEXT_MEMORY, GLOBAL_UID, HOST, IDENTIFICATION_TYPE, INSTANCE, INSTANCE_NAME, IP_ADDRESS, ISDBA, LANG, LANGUAGE, MODULE, NETWORK_PROTOCOL, NLS_CALENDAR, NLS_CURRENCY, NLS_DATE_FORMAT, NLS_DATE_LANGUAGE, NLS_SORT, NLS_TERRITORY, OS_USER, POLICY_INVOKER, PROXY_ENTERPRISE_IDENTITY, PROXY_GLOBAL_UID, PROXY_USER, SERVER_HOST, SERVICE_NAME, SESSION_USER, SESSION_USERID, SESSIONID, SID, STATEMENTID, TERMINAL
e.g.
SQL> select SYS_CONTEXT ('USERENV', 'SESSION_USER') from dual;
-- HR
e.g.
SQL> select SYS_CONTEXT ('USERENV', 'CURRENT_SCHEMA') from dual;
-- HR
Deprecated parameters
AUTHENTICATION_TYPE, CURRENT_USER, CURRENT_USERID, EXTERNAL_NAME
Extra for sys_context
Link
Ref: http://docs.oracle.com/cd/B19306_01/server.102/b14200/functions165.htm