I highly recommend Martin Kleppmann's Designing Data Intensive Applications(http://dataintensive.net http://dataintensive.net). It will not only help you under

I highly recommend Martin Kleppmann's Designing Data Intensive Applications(http://dataintensive.net http://dataintensive.net). It will not only help you understand what's "SQL" and "NoSQL" data stores, it also covers the differences between each of them, what problems they are designed to solve, how they try to solve it, and if it'll help with your problems as well.