Both MongoDB and CouchDB are document-oriented datastores. They both work with JSON documents. They both are usually thrown into the NoSQL bucket. They’re both hip. But that’s where the similarities, for the most part, stop.
When it comes to queries, both couldn’t be any more different.
They differ even in the implementation and behavior of MapReduce.
Original title and link for this post: CouchDB and MongoDB: Quering (published on the NoSQL blog: myNoSQL)