(disclamer: I have more than a decade experiences in doing SQL)

I would say Mr. Joe Celko's "SQL for smarties" (and basically anything he has written (look him up for references)....

I have had the opportunity to talk to mr. Celko, and he added (as I asked him what he thought was the best database-book) the "Manga Guide to Databases" (seriously!), I am reading it now (but I am only in the second chapter), and it seems very good...

If you need a good database which honors the standard behaviour closely and has super documentation (and very clean codebase), take a look at Postgresql. The fact that is is free and open source (bsd licensened) does not hurt at all :)