In an ever-changing world, the data surrounding relational and non-relational databases is no different. While there are proponents for both, it seems to be a case by case basis for which is best for a particular environment. And, with the pace of innovation, the answer can be swayed on a frequent basis. With all that being said, the numbers don't lie, and there is evidence of a shift that is occurring.
While most of the stalwart SQL related databases (MSSQL, Oracle RDBMS, DB2, etc.) remain stagnant, there has been a decline in interest for MySQL. Might seem surprising given the fact that one of the core components of the original LAMP stack is losing ground. How could that be the case? In essence, a lot has changed since it came into prominence. Most importantly, in my opinion, is that it was purchased by Oracle. No longer an independent entity, you have one company controlling two prominent database choices. Is it possible for Oracle to be unbiased and treat each on its own merits? Perhaps. Only the folks inside the company know the true answer to that. Whatever the answer may be, it goes without question that the momentum that MySQL once had has been subdued.