DBTIMEZONE
There're 2 ways to check the time zone of a database.
Database Property
Since DBTIMEZONE is actually a property of database, we may query DATABASE_PROPERTIES like this:
SQL> select property_value from database_properties where property_name = 'DBTIMEZONE';
PROPERTY_VALUE
--------------------------------------------------------------------------------
+00:00
Database Function
There's a same name function called DBTIMEZONE can be use to display the database timezone.
SQL> select dbtimezone from dual;
DBTIME
------
+00:00
In most cases, the database time zone is set to UTC time zone.
Database time zone usually works with TIMESTAMP WITH LOCAL TIME ZONE column, which is a datetime type and does not store time zone information internally.
Oracle recommends that you set the database time zone to be a generally used one, UTC (0:00). Don't change it if you didn't have a good reason to do it.
For normal operations, you may need to check the session time zone.