RMAN uses the recovery catalog--or target database control file if no recovery catalog is available--to select the best available backup sets for use in the restore operation. When multiple choices are available, RMAN uses the most current backup sets, taking into account whether you specified any limits.
By selecting , RMAN selects the most current backup set to restore.
Selecting limits the selection to those backup sets that would be suitable for performing a point-in-time recovery.
The upper limit may be specified by time, SCN, or log sequence number, as follows: