I asked one of the developers about that and he said that the sql function is in there for diagnostic purposes. It's not advisable to use that unless you know what you are doing because you can change alot of your data with one little bit of code. You may not even know what you changed.
If you are interested in sql in general there are many websites on the internet about it. Just go to google and do a search on sql. Here is an example http://www.1keydata.com/sql/sql1.html.