A friend call me this morning, ask which database I know? I thought I am going to answer him, I don't know much about database, because I am a programmer and not database administrator. I suddenly know what he means, so I told him I know Postgresql, Informix and Oracle.
All these database are installed and used in our development environment, I have installed most of it by myself many years ago, mostly old version which are outdated, eg. Informix 5(?), Oracle 8.
Install Oracle 8 on Linux operating system is not an easy task, you need to patch the system, at the middle of the installation process. I think Oracle people don't write good installer on Linux, may be they don't have good software people who familiar with Linux development, I hope they have improve by now.
Normally programmer focus on programming, we left SQL queries to the database administrator. We don't know much about database optimization, it need a professional to do it. That is the ideal case, normally we have to play both roles.
I know how to compile postgresql and mysql database, does it consider a special skills? I even do software packaging for postgresql on Linux and Solaris. I know some other database like Cloudscape, if you have forgotten, it is a embedded database purely written in java, and is open source. Cloudscape can store a java object as a data field, eg. a java method (function). Cloudscape source code has pass to apache, will be Derby next time.
I know another database(?) call netisam (from Sun, and no more supported by Sun), I bet not one heard it before, even if you know about it, you should have erase it from you memory, because netisam don't support JDBC, ODBC, even SQL queries! (I put a question mark after the database) and no more supported by Sun. Then how it works? If you have worked on Informix ESQL/C before, you should know, netisam is just an embedded database.
The worst thing about netisam is, I don't find a open source replacement for it!