I really enjoy database design and the whole concept of managing data semantically and all the logic that comes with it.
My knowledge level when it comes to databases is
being just a student of Databases I can only speak from my limited scope but I can suggest two sites that may help...
http://database-programmer.blogspot.com/2008/09/comprehensive-table-of-contents.html
This is Kenneth Downs site, he goes from the very basics if SQL and delves into more complex subjects. The man has written a framework around DB's after all.
Another one is High Scalability...
http://highscalability.com/
They get into every realm of DB's.
Hope this helps.