Have you seen the map of all the different databases on the market today from 451 Group?
There used to be just a few relational databases: DB2, MYSQL, Oracle, SQL Server, Sybase.
Now, there are actually twenty (20) different categories of databases! And well over 100 different vendors.
How many can you name?
How many have you installed?
How many have you used?
The full article is here:
http://blogs.the451group.com/information_management/2013/06/10/updated-database-landscape-map-june-2013/