SYS_CONTEXT

Oracle has a very useful built-in function called SYS_CONTEXT. The syntax of this function goes like this:

SYS_CONTEXT ( 'namespace' , 'parameter' [, length] )

SYS_CONTEXT returns the value of parameter associated with the context namespace. You can use this function in both SQL and PL/SQL statements.

What makes this function more interesting is the fact that Oracle provides a built-in namespace called USERENV with predefined parameters, which describes the current session. Go ahead and run the following query:

select 
    sys_context('USERENV','AUTHENTICATION_TYPE') 
    ,sys_context('USERENV','CURRENT_SCHEMA') 
    ,sys_context('USERENV','CURRENT_SCHEMAID') 
    ,sys_context('USERENV','CURRENT_USER') 
    ,sys_context('USERENV','CURRENT_USERID') 
    ,sys_context('USERENV','DB_DOMAIN') 
    ,sys_context('USERENV','DB_NAME') 
    ,sys_context('USERENV','HOST') 
    ,sys_context('USERENV','INSTANCE') 
    ,sys_context('USERENV','IP_ADDRESS') 
    ,sys_context('USERENV','ISDBA') 
    ,sys_context('USERENV','LANG') 
    ,sys_context('USERENV','LANGUAGE') 
    ,sys_context('USERENV','NETWORK_PROTOCOL') 
    ,sys_context('USERENV','NLS_CALENDAR') 
    ,sys_context('USERENV','NLS_CURRENCY') 
    ,sys_context('USERENV','NLS_DATE_FORMAT') 
    ,sys_context('USERENV','NLS_DATE_LANGUAGE') 
    ,sys_context('USERENV','NLS_TERRITORY') 
    ,sys_context('USERENV','OS_USER') 
    ,sys_context('USERENV','SESSION_USER') 
    ,sys_context('USERENV','SESSION_USERID') 
    ,sys_context('USERENV','SESSIONID') 
    ,sys_context('USERENV','TERMINAL') 
from dual

Amazing , you can Use this Function in Oracle Security .

Enjoy

Thank you
Osama mustafa