Excerpt from a long-view DBMS/SQL/etc. perspective (thanks to Periscope for the reference)
"As various NoSQL databases matured, a curious thing happened to their APIs: they started looking more like SQL. This is because SQL is a pretty direct implementation of relational set theory, and math is hard to fool.
To paraphrase Paul Graham’s unbearably smug comment about Lisp: once you add group by, filter, & join, you can no longer claim to have invented a new query language, only a new dialect of SQL. With worse syntax and no optimizer.Cache is the new RAM | MemSQL - The Database for Speed, Scale & Simplicity
Because we had taken this strange detour away from SQL, crucial bits missing from most of the systems are a storage engine and query optimizer designed around relational set theory. Bolting that on later led to severe performance hits. For the ones that got it right (or papered it over by being resident in RAM) there were other bits missing like proper replication."