One free, handy reference can be found online.... for basic stuff,
www.sqlcourse.com, and for more in-depth stuff, there's
www.sqlcourse2.com. There's also an SQL interpreter on the page, so you can try out the commands yourself pretty easily. It mostly covers cross-platform SQL, not so much DB-specific commands.
Why buy a $50 technical manual which rapidly becomes obsolete, when you have access to gobs of webpages full of constantly updated information? I know, I prefer pulp myself, despite the fact that it's an irrational preference when it comes to computer technical manuals, and I have to fight it constantly.