[teknomage1]

Why not using an existing database? SQLite is very impressive as are mysql and postgres.

If you're set on writing one yourself, realize that modern relational databases are very complicated. In general you take over a chunk of diskspace and write a "filesystem" to store the various tables and columns. You then have to be able to read them into to memory efficiently and write them back to disk in a reliable manner as they change. You also have to have a way to communicate with the database, so you'll need some client server code. Also you probably want to conform to the SQL standard.