How to: Translate SQL to MongoDB MapReduce

I keep hearing people complaining that MapReduce is not as easy as SQL. But there are others saying SQL is not easy to grok. I’ll keep myself away from this possible flame war and just point you out to this SQL to MongoDB translation PDF put together by Rick Osborne and also his post providing some more details.

As regards the SQL and MapReduce comparison, here’s what Rick has to say:

It seems kindof silly to go through all this, right? SQL does all of this, but with much less complexity. However, this approach has some huge advantages over SQL:

1. Programmers who don’t know SQL or relational theory may find it easier to understand and get using quickly. (Newbies especially, such as my students.)
2. The map and reduce functions can be heavily parallelized on commodity hardware.

It’s really that second one that is the key.

I’d also like to share something that I’ve learned lately: SQL parallel execution is supported in different forms by some RDBMS. So at the end of the day, it will probably become just a matter of what fits better the problem and your team.