Database Theory

Why is it so hard to find a good technical book on the theory database design? There are like a million books with titles like 'Learn SQL in 24 Hours!' which are good for finding shitty cookie-cutter code - but almost nothing that gives you a deep understanding of what is going on. Okay - granted I have devoted my searches to ebooks I can download using bittorrent, but still....

I think things started turning to shite when those ' for Dummies' books first came out. To this day I cringe whenever I see them at Borders.