Originally posted by sambavan
To get this information you can check the oraInventory/Patches this would reveal you the patches that you have applied so far on to the database.
I stress again: this is true only if the pach has been applied through Universal Installer.

But some "minor" patches can not be applied like this - for them to be "installed" you simply has to copy bunch of exec and library files over the old ones. To keep track of such paches installed there is no other way than to have a good memory or good "document everything" habit.

And to answer jt: I don't think there would be a problem to reapply same patch again, unless it is lower than the highest patch allready applied. If the patch has to be installed by Oracle Universal Installer then the Installer will complain anyway.