Find the patches applied to your database

SQL> select ACTION_TIME,ACTION,VERSION,ID,COMMENTS from registry$history;

ACTION_TIME ACTION VERSION ID COMMENTS
-------------------- -------------- ---------- ---------- --------------------
13-NOV-09 05.54.51.9 UPGRADE 10.2.0.4.0 Upgraded from 10.2.0
01116 PM .1.0

The above query will display the series of upgrades/downgrades done on your database.


(OR)

$ORACLE_HOME/OPatch/opatch lsinventory