System Change Number
Some DBAs will schedule a cron job to capture System Change Number (SCN) periodically to save as a Timestamp/SCN mapping reference. To achieve this goal, you can try the following statements.
CURRENT_SCN
We cam query the value CURRENT_SCN from V$DATABASE.
SQL> ALTER SESSION SET NLS_TIMESTAMP_TZ_FORMAT = 'YYYY-MM-DD HH24:MI:SS.FF TZH:TZM';
Session altered.
SQL> COLUMN SYSTIMESTAMP FORMAT A35;
SQL> SELECT systimestamp, current_scn FROM v$database;
SYSTIMESTAMP CURRENT_SCN
----------------------------------- -----------
2011-07-28 15:56:51.620279 +08:00 3094334
GET_SYSTEM_CHANGE_NUMBER
Or use function DBMS_FLASHBACK.GET_SYSTEM_CHANGE_NUMBER directly:
SQL> SELECT systimestamp, dbms_flashback.get_system_change_number CURRENT_SCN FROM DUAL;
SYSTIMESTAMP CURRENT_SCN
----------------------------------- -----------
2011-07-28 15:57:16.758427 +08:00 3094388
Please note that, the function SYSTIMESTAMP accepts NLS_TIMESTAMP_TZ_FORMAT, not NLS_DATE_FORMAT or NLS_TIMESTAMP_FORMAT.
TIMESTAMP_TO_SCN
Function TIMESTAMP_TO_SCN can be used to convert timestamp to SCN. For example:
SQL> SELECT systimestamp, timestamp_to_scn(systimestamp) CURRENT_SCN FROM DUAL;
SYSTIMESTAMP CURRENT_SCN
----------------------------------- -----------
2011-07-28 15:57:16.758427 +08:00 3094388
Further reading: How to Map Timestamp to SCN or Vice Versa