FIXED_DATE Init.ora parameter

Setting this parameter to a specified timestamp will make the time constant for the database engine (the clock will not tick) FIXED_DATE is a dynamic parameter and can be changed using the ALTER SYSTEM command.

SQL> ALTER SYSTEM SET FIXED_DATE='2009-09-22-13:00:00';

Once you set parameter, the value will be returned when ’sysdate()’ is used in the queries/application.
To see the server time, you can use systimestamp.

Eg:

SQL> set lines 100
SQL> select sysdate, systimestamp from dual;

SYSDATE					SYSTIMESTAMP
-------					-------------------------
2009 09 22 13:00:00 	10-DEC-09 03.01.41.142940 AM -06:00

This is usually used for testing/development purposes, when the application logic depends on a specific date/time combination.

To set the date back to the ’system’ clock, set the parameter to ‘none’

SQL> alter system set fixed_date='none';