In my experience, its better to find any of the big databases in any reasonably sized corporation. as I know "exclusive Oracle" shops that also supported a couple of SQLServer databases, and "exclusive IBM shops" that had Oracle or Sybase installs hanging around. Learn basic SQL anywhere and then pick up the administration for one or two of the big guys (Oracle, SQL Server, Sybase, DB2) and the free/open ones (MySQL, postgreSQL, etc.) are always great for learning and in some business applications.