There used to be a public link to the JTC 1/SC 32 working drafts of 9075:2003, but the link I had has not worked since they started on the post-2003 revisions. Given that there are publicly available copies of many of their other specifications (11179-1:2004, for example), I'm wondering if any one knows of any ways to legally get access to the ISO/IEC 9075 specifications. Perhaps there is a link to the working drafts, or a Foundation that provides access to it for something less than the roughly $3000 USD it would cost me to learn SQL from the standards body instead of relying on implementation-specific books and documentation.
The formal spec is about the worst choice you can make for a resource if your purpose is (quote) "to learn SQL".
I'd advise you to learn SQL "the normal way", and keep it in the back of your head that there is such a thing as a standard version of the language, and keep it in the back of your head that many implementations can get really rather grotesque in their deviations from and omissions from and extensions to the standard.
"and wanted to branch out to understanding which parts of those engine-specific dialects are actually part of the standards, and which parts are not."
That sheds a bit of an other light on your question. The following, though not entirely "gratis", but much less expensive than the full print, might be of help :
"The five parts of SQL:2011 were published yesterday (which for my current time was 2011-12-15). The documents can be found in the ISO web store using:
The consolidated CD (containing the 2011 edition of parts 1, 2, 4, 11, and 14 and the 2008 edition of parts 3, 9, 10, and 11) is listed at CHF 238,00."
C. J. Date, Hugh Darwen
A Guide to the SQL Standard
tutorial to the SQL92 Standard from two prominent database experts