Finding Oracle Session ID (SID)
The current Oracle session ID is often used when you want to analyze data from v$session and similar views.
Recipe #1 - Finding the Oracle Session ID
There are several ways to get the Oracle session ID, here's the probably most used version:
SELECT SYS_CONTEXT('USERENV', 'SID') FROM DUAL;
Recipe #2 - combining Session ID and v$session
Here's a simple example showing you how to use the current session ID in combination with v$session:
SELECT osuser, program FROM v$session WHERE sid=SYS_CONTEXT('USERENV', 'SID');
Recipe #3 - alternative ways to get session ID
just in case you wonder, there are more ways to get the current session ID:
SELECT sid FROM v$mystat WHERE ROWNUM = 1;
You could also use DISTINCT, GROUP BY among a few other commands to get just a single row instead of ROWNUM but that's doesn't really change anything.
If you want to use something more complicated, go for this:
SELECT TO_NUMBER(SUBSTR(DBMS_SESSION.unique_session_id, 1, 4)) sid FROM dual;