Which database for survey app I need to build a very simple mobile survey app. The app will ask for different questions where people can give one of 3 possible answers, which will be always "yes", "no" or "maybe".   

To save these questions and answers I need a simple scheme with 2 tables like:


question(id:int, question:varchar, createdAt:timestamp)
answer(id:int, questionId:int, answer:enum, createdAt:timestamp)


I'm asking myself if I should go for a good ol' MySql for that or if I should choose a NoSQL database like MongoDB.

I have following minimal requirements:


Concurrent (non locking), fast inserts should be possible
Fast read queries to do some analytics
Indexing of table data
Several millions of entries should be no problem (hard disk space is the limit :)
Backups should easily be possible
Convenient date/time functions


I think MySQL should do the trick, but I've never tried out databases like MongoDB before. The app will leverage JSON as data exchange format and I know that MongoDB plays quite well with that. 

Any advice is much appreciated!

Best regards
PostgreSQL is often overlooked but might be worth your attention.  It supports MVCC for concurrency, can do analytic SQL queries easily, supports indexes, scales up well enough, can do hot backups, supports date functions, and even has JSON data types.  Binary JSON (aka: JSONB, BSON) is being added to newer versions, which will give you the ability to index on JSON content and have improved analytic function &amp; performance.

Check this out article on Phoronix:

Binary JSON Support Added To PostgreSQL, Competes With MongoDB
http://www.phoronix.com/scan.php?page=news_item&amp;px=MTY0MTU