After seeing this image:
http://2.bp.blogspot.com/_T-uXeKcGTnM/TIdoKBGwk9I/AAAAAAAABcs/CLW3_cRlN78/s1600/tumblr_kxovt0VLZy1qappj8.png
I wonder is exists any tool for translating SQL querys into MongoDB map/reduce query model??
Larger version of the image: http://rickosborne.org/download/SQL-to-MongoDB.pdf
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/
Update to the question asked in Jan 2011:
A couple of sites exist now to convert sql to mongodb.
Convert MySQL Queries to MongoDB Syntax
http://www.querymongo.com/
And
Convert sql to mongodb
http://klaus.dk/sqltomongodb/
The simple answer: Yes. Hibernate OGM - JPA for NoSQL.
JPA is Java API for mapping objects to data stores.
It includes JPQL, a query language similar to SQL which adds the OOP concepts. It's not SQL, but you don't want pure SQL - that was designed for the relational paradigm.
Hibernate OGM proposes to simplify the programming model by embracing JPA/Hibernate APIs and semantics to store data in NoSQL stores like JBoss Enterprise Data Grid instead of the traditional RDBMS. (source)
Also see this Hibernate OGM: JPA for NoSQL talk by Hardy Ferentschik
Recently I happened to see this website mongoquery.com, you can try it.
Just to add to the last comment
re:The simple answer: Yes. Hibernate OGM - JPA for NoSQL.
JPA is Java API for mapping objects to data stores.
It includes JPQL, a query language similar to SQL which adds the OOP concepts. It's not SQL, but you don't want pure SQL - that was designed for the relational paradigm.
There is a company called UnityJDBC that has released a JDBC driver for Mongo that allows you to run SQL queries against mongo in any java application that supports JDBC.
you can download this driver free at
http://www.unityjdbc.com/mongojdbc/mongo_jdbc.php
hope this helps
You can also http://teiid.org which gives full range of SQL based access to MongoDB. You can use SQL through JDBC/ODBC or use REST/ODATA based access to MongoDB. Teiid uses MongoDB's aggregation framework to provide advanced SQL MongoDB query conversation.