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.
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):
A draft of the standard text is available at http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt.