This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Yes you can install multiple database products on one machine because they usually use different ports to allow client connections. I have MySQL and PostgreSQL installed on most of my systems, and in one case also have SQL Server.