When it comes to security they are pretty much equal. That is as long as they are set up properly. MySql has a max database size of 256T and oracle like to process in blocks, to see there limits check out this Oracle link
Register Hereor login if you are already a member
This is basically depends on database's own mechanism. How they offer to enter their own interface for starting work. While SQL Server offers GUI method to start working. No, Oracle & MySQL, both provide a good security system. Generally, Oracle can use for a large database system. By the way, are you going to design database design for your organization? Or it is a part of your home work?