ISO SQL is a rather weak standard.
First you can not get it unless you pay for it, which is not a good thing if you want your standard to be succesful. You can find draft versions of the latest SQL 2011 on the web however.
Second there is no official independent compliance verification.
Appendix B of the Oracle Database SQL language reference gives a detailed overview of Oracle standard compliance.
In oracle you can set the FLAGGER variable, to verify whether your command complies with the standard. It only checks compliance with the ISO SQL/92 standard though:
Finally, here's a neat overview of compatibility of SQL statements for the most popular databases.