SQL zum MongoDB Query Converter
The simple anwser? No.
The slightly more complex anwser is some people have had luck translating more complex SQL to Mapreduce functions ...
http://rickosborne.org/blog/index.php/2010/02/08/playing-around-with-mongodb-and-mapreduce-functions/
http://rickosborne.org/blog/index.php/2010/02/19/yes-virginia-thats-automated-sql-to-mongodb-mapreduce/
However, that said ... generally speaking you might as well learn mapreduce properly because if the data is in MongoDB already ... you'll really need to know how to properly query MongoDB to get anything meaningful done!
MongoDB has wonderful and helpful docs http://www.mongodb.org/display/DOCS/Advanced+Queries
As well as an easy to use online tutorial: http://try.mongodb.org/
Santino