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Oracle: ALTER SESSION SET TIME_ZONE …

Determine the session's current time zone:

select
   sessiontimezone
from
   dual;
--
-- SESSIONTIMEZONE                                                            
-- ---------------------------------------------------------------------------
-- Europe/Berlin

Modify the session's time zone:

alter session set time_zone ='America/New_York';
--
-- Session altered.

select
   sessiontimezone
from
   dual;
--
-- SESSIONTIMEZONE                                                            
-- ---------------------------------------------------------------------------
-- America/New_York

Modify relative to GMT:

alter session set time_zone = '-03:00';

select
   sessiontimezone
from
   dual;
--
-- SESSIONTIMEZONE                                                            
-- ---------------------------------------------------------------------------
-- -03:00

Evaluate systimestamp in session's time zone:

select
   to_char(systimestamp                             , 'yyyy-mm-dd hh24:mi:ss (tzr)') ts1,
   to_char(systimestamp at time zone sessiontimezone, 'yyyy-mm-dd hh24:mi:ss (tzr)') ts2
from
   dual;
--
-- TS1                           TS2                         
-- ----------------------------  ----------------------------
-- 2023-08-22 08:17:31 (+00:00)  2023-08-22 05:17:31 (-03:00)

Trying to set the session's time zone to an unrecognized value:

alter session set time_zone = 'Europe/Berne';
--
-- ORA-01882: time zone region not found

Find available time zone values:

select * from v$timezone_names;

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