Oracle Flashback Query Using AS OF TIMESTAMP

Since Oracle 9i Release 2, you can use "AS OF SCN | TIMESTAMP" flashback query to query the "before" data of a changed table. It's useful to find the changes you made or recover errors.
I used TIMESTAMP more often and found it simple but efficient. I'll show some examples below.

SQL> select salary from employees where employee_id = 100;
SALARY
----------
24000

SQL> update employees set salary = salary * 1.05 where employee_id = 100;
1 row updated.

SQL> commit;

SQL> select salary from employees where employee_id = 100;
SALARY
----------
25200

Here shows the way to query the "before" data of yesterday:

SQL> select salary from employees AS OF TIMESTAMP sysdate - 1 where employee_id = 100;
SALARY
----------
24000

To show ten (10) minutes ago:

select salary from employees AS OF TIMESTAMP sysdate - 10/60/24 where employee_id = 100;

Or you can use function SYSTIMESTAMP instead of sysdate.

select salary from employees AS OF TIMESTAMP (SYSTIMESTAMP - INTERVAL '1' DAY) where employee_id = 100;
select salary from employees AS OF TIMESTAMP (SYSTIMESTAMP - INTERVAL '10' MINUTE) where employee_id = 100;

To recover the change:

SQL>update employees e1 set salary =
( select salary from employees AS OF TIMESTAMP sysdate - 1 e2
where e2.employee_id = e1.employee_id )
where employee_id = 100;
1 row updated.

SQL> select salary from employees where employee_id = 100;
SALARY
----------
24000

You may sometimes want to save the before data to a temporary table, then compare and reccover.

create table tmp_employees nologging as select * from employees AS OF TIMESTAMP sysdate - 1;

The SELECT ... AS OF will not work after the table structure changes or table truncation.

SQL> truncate table tmp_objects;
Table truncated.

SQL> select count(*) from tmp_objects as of timestamp sysdate - 1/24/60;

ORA-01466: unable to read data - table definition has changed