This is a very good read:
http://typicalprogrammer.com/?p=14
I especially like the following:
Because most of what programmers do has no theoretical basis or system of proof, programmers back away from anything that looks like hard math. Failure to understand and appreciate relational theory has launched countless bad databases (and thousands of witless articles condemning SQL). The idea that there is a right way to design a normalized database–and that the wrong ways are provably wrong–is alien to most programmers. Database management doesn’t come down to a matter of opinion like OOP class hierarchies or coding style.
At times there are calls to get rid of the ‘traditional’ RDBMSs and replace them with…object oriented databases, MapReduce, etc. Almost all of these calls are misguided.
When either Oracle and/or Microsoft releases an object oriented database, then you will know when you can ignore them (for the most part, there are always special cases). Until then, you need to know how to deal with a database.
Good stuff.