MySQL vs Oracle
This juxtaposition comes up from time to time and brings to mind the comparision of dolphins with nuclear-powered submarines.
While it is possible to train dolphins for use against maritime targets this is a task generally better suited to purpose-built ordnance. Dolphins are better at jumping through hoops in aquariums.
If you find your application works as equally well on Oracle as it does on MySQL, then you are vastly underutilising Oracle and probably paying for it as well.
If you are looking for Oracle-level capability but with the advantages of Open Source, take a look at Firebird or PostgreSQL. Neither are anywhere near Oracle's heavyweight status (which is not necessarily a disadvantage), but unless you have specific requirements, they probably have virtually all the features you will need.