in reply to
Perl and Database
If the goal is to learn and to improve your CV, I would install all these systems.
But definitely include Oracle: it's pretty much the gold standard of database systems, and there is always well-paid work.
If you also install the free/opensource systems PostgreSQL, MySQL and SQLite, you can learn how to write programs that talk to the different systems in the same way (=with the same SQL statements). This way you'll learn the differences and specific strengths of each system.