Why is Riak TS considered as a NoSQL database when it needs a predefined schema for tables? This schema even cannot be changed! Source: documentation
I think that some people may think that when Riak TS is built on Riak KV, then it is a NoSQL database, but that each row maps to a key-value pair do not bring a NoSQL advantage. If the Riak TS is not schema-less, it should not be considered as a NoSQL database in my opinion.
Do I understand it wrong? Why is it officially considered as NoSQL?
SQL is not only about having a table schema. First the query language supported is only a tiny subset of SQL. Then, Riak TS doesn't provide things that you'd expect from other traditional SQL DB, like ACID, transactions, etc. Also, it's not really a normal DB as you can't update values.
So it doesn't make sense to define it as an "relational DB" or "SQL database". But it doesn't really make sense to define it as a "NoSQL DB" :) I think the best definition is a "TimeSeries distributed DB"