We all love open source software. Wouldn’t it be great if international standard documents such as the SQL standard would be open too?
As a matter of fact: they are!
However, they are not free—just public. Very much like open source software is not necessarily free. Too often, we neglect these differences. Just because we have to pay for the standard doesn't mean it is secret.
A download of the most relevant part of the SQL standard—part 2—is available for EUR 180 at Austrian Standards. The 2011 version can still be bought for USD 60 at ANSI. It might pay off to check the prices at other ISO members. The SQL standards is not free, but affordable.
Nevertheless there are some free resources that can help you answering questions about the SQL standard:
Part 1 can be downloaded free of charge from ISO (look for SQL).
Drafts of all parts are linked as “SQL:20nn Working Draft Documents” at http://www.wiscorp.com/SQLStandards.html.
Recommended articles (PDF):
Browsable BNF grammar of Part 2.
A draft of the standard text is available at http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt.