yeah, you're right, $5 does sound a little dodgy
the one you linked is $27, though, and from the table of contents it looks comprehensive
however, there are plenty of free non-video sql tutorials out there (plenty?? hunnerts and hunnerts of them!!) and some of them are excellent
however, i haven't looked at tutorials for years, so i cannot recommend any at this time
if you really don't want to google, and are willing to pay a modest amount, may i suggest an e-book?