SESSIONTIMEZONE
While DBTIMEZONE is to check the database time zone, the built-in function SESSIONTIMEZONE is to check the exact time zone in the current session.
SQL> select sessiontimezone from dual;
SESSIONTIMEZONE
---------------------------------------------------------------------------
-04:00
In fact, the session time zone usually follows the time zone of the operating system where we initiate the session. Let's check the time zone in Linux server.
[oracle@test ~]$ timedatectl | grep "Time zone"
Time zone: America/New_York (EDT, -0400)
They're the same.
If this is not what we want, we need some ways to update time zone in the current session.