Oracle Backup & Recovery Techniques - Oracle 10g Database Administration Concepts and Implementation Made Simple - page 333

SQL> show parameter UNDO;

NAME TYPE VALUE

----------------------- -------------- -----------

undo_management string AUTO

undo_retention integer 900

undo_suppress_errors boolean TRUE

undo_tablespace string

undotab

How to set UNDO_RETENTION?

The UNDO_RETENTION initialization parameter is defined in
seconds and to set it to two days use the following statement.

SQL>ALTER SYSTEM SET UNDO_RETENTION = 172800;

Flashback Query is a SELECT query with an AS OF
TIMESTAMP clause.

SQL> SELECT *
FROM emp
AS OF TIMESTAMP ('15-JUL-04 14:50:58','DD-MON-YY
HH24:MI:SS');

OR

SQL> INSERT INTO emp_temp

(SELECT * FROM emp AS OF SCN 1897209);

This statement will insert all the recorded changes in undo
tablespace since SCN into emp_temp table.