I want have Linux based database server. Is it possible to connect from computer that is running Oracle VM Virtualbox to OS running inside virtual machine?
Is it possible to connect to your VirtualBox VM from the machine that is running the VirtualBox hypervisor? Sure. You can even connect to it from other machines on your network (by using a bridged-mode virtual network adapter).
How will the performance be if you try to run a database with any kind of load in a VM? Bloody awful.