Check the comparison page on their site. It's free as in beer, and open source. The lady I spoke to had no idea what I meant when I asked her under which license it's offered. She said there was no license.
So of course I asked her if that meant I could sell it, as that question always elicits some kind of response. She said no I couldn't sell it. I asked her, if there were no license, what would keep me from selling it, and her reply was that it's their own build of MySQL. So of course whether their employees know it or not, it's under the same license (GPLv2), because of the terms of GPLv2 it must be. (And then of course you can sell it, as long as you also deliver the source code under the GPLv2 rules.)
I didn't ask her if they supply the source code; I should have.
Jeff