The time zone for the database is the database time zone.
The time zone set for your database session is the session time zone.
The database time zone is set by the TIME_ZONE database parameter.
The setting of the TIME_ZONE parameter is in init.ora or spfile.ora file.
By default, the session time zone is the same as the database time zone.
You can change the session time zone using the ALTER SESSION statement to set the TIME_ZONE parameter.
Setting the session time zone doesn't change the database time zone.
For example, the following statement sets the local time zone to Pacific Standard Time (PST):
ALTER SESSION SET TIME_ZONE = 'PST';