How to use SYS_CONTEXT to display user information

Oracle provides a built-in namespace called USERENV, which describes the current session.

The function SYS_CONTEXT can be used to return the value of parameter associated with the context namespace. You can use this function in both SQL and PL/SQL statements.

You can use the SYS_CONTEXT to retreive userinformation from the namespace USERENV, some examples below:

col "OS user" format a20
col "Current schema" format a20
col "Identification type" format a20
col "IP" format a20
col "Host name" format a20
col "SID" format a10
col "Service" format a20
SELECT SYS_CONTEXT ('userenv','OS_USER') "OS user", 
       SYS_CONTEXT('userenv','CURRENT_SCHEMA') "Current schema",
       SYS_CONTEXT('userenv','IDENTIFICATION_TYPE') "Identification type",
       SYS_CONTEXT('userenv','IP_ADDRESS') "IP",
       SYS_CONTEXT('userenv','HOST') "Host name",
       SYS_CONTEXT('userenv','SID') "SID",
       SYS_CONTEXT('userenv','SERVICE_NAME') "Service"
FROM DUAL;

Executed from a remote session, logged into the database as user SCOTT, the output from the query above will be:

OS user	Current schema	Identification type	IP	Host name	SID	Service
SCOTT	SCOTT	LOCAL	192.168.1.2	MYDOMAIN\MYCLIENT	170	myservice.mydomain.com

To find the serial# of your session, you will need to query the v$session dynamic performance view. you need to have SELECT privileges on the V$SESSION view to use this query, so first, a grant is needed.

SQL> show user
USER is "SYS"

GRANT SELECT ON V_$SESSION TO SCOTT;

Now, as user SCOTT, you can execute the query

SELECT SID, SERIAL#
FROM V$SESSION
WHERE SID=SYS_CONTEXT('USERENV','SID');


Source: Oracle Documentation The 12.2 SYS_CONTEXT documentation can be found here