After developing software for about 5 years now, I have spent probably atleast 20% and perhaps up to 40% of that time simply making a RDBMS able to save and retrieve complex object graphs. Many times this resulted in less than optimal coding solutions in order to make something easier to do from the database side. This eventually ended after a very significant amount of time spent in learning NHibernate and the session management patterns that are part of it. With NHibernate I was able to finally eschew the large majority of 100% wasted time of writing CRUD for the 1000th time and use forward generation of my database from my domain model.
Yet all of this work still results in a flawed model where my database is merely the best attempt by SQL to imitate my actual object. With document databases this is no longer the case as the object becomes the document itself instead of merely emulating the object through tables and columns.
At this point I’m really starting to question why would I ever need SQL again?
What can really be done substantially better with SQL than a document database?
I know this is somewhat of leading into a apples to oranges comparison especially when you factor in the various types of NoSQL databases having widely different feature-sets but for the sake of this argument base it on the notion of NoSQL databases can inherently query objects correctly and not on the limitations of a key value store. Also leave out the reporting aspect as that should generally be handled in a OLAP database unless your answer includes a specific reason you would not use a OLAP database for it.
My key question was where would a SQL database really outshine a document database and from all the responses there really doesn’t seem to be much.
Given that NoSQL databases come in just as many variations of types of databases as relational that both match all or some parts of ACID depending on which database you use that at this point they are basically the equitable for solving problems.
After this the key differences would be tooling and maturity which SQL databases have a much larger grasp in for being the established player but this is how it is for all new technology.