It all depends on what you want to do, how the database is used & setup, will each game client need its own database or will all the clients connect to a central database on your game server or both.
Your programming skills will also play a role in what you want to do because some of these databases are harder to use than others.
Oracle would probably be overkill for most things and prohibitively expensive.
Database Programming in C resources
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MySQL Database C API programming tutorial
[Html]
http://zetcode.com/tutorials/mysqlcapitutorial/Berkley DB embedded C API
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Getting Started with Data Storage:
[Pdf]
http://www.oracle.com/technology/docume ... -C-GSG.pdf[Html]
http://www.oracle.com/technology/docume ... index.htmlGetting Started with Transaction Processing:
[Pdf]
http://www.oracle.com/technology/docume ... -C-Txn.pdf[Html] Getting Started with Transaction Processing
Getting Started with Replication:
[Pdf]
http://www.oracle.com/technology/docume ... -C-GSG.pdf[Html]
http://www.oracle.com/technology/docume ... index.htmlReferance Guide:
[Html]
http://www.oracle.com/technology/docume ... f/toc.htmlProgrammatic API:
[Html]
http://www.oracle.com/technology/docume ... frame.htmlHamster embedded DB
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[Site]
http://hamsterdb.com/index[PDF]
http://hamsterdb.com/public/dl/tutorial.pdf[Examples]
http://hamsterdb.com/documentation/samplesSqlite embedded database.
http://souptonuts.sourceforge.net/readm ... orial.htmlI also maintain a list of C programming resources, you might find some useful info there.
http://www.gtkforums.com/viewtopic.php?t=988 Get the database aspect of your game done and then you could worry about optimization.
Hope that helps.