SQL = structured query language. It's just an interface to access data. All relational databases offer it but so do many other non-relational systems. This means using SQL to read/write data is completely separate from having relational functionality like joins.
May I ask that we shouldn't use the term Document Store or Document <anything> for JSONish data as used by Mongo, and by extension AWS "DocumentDB" and Cosmos DB. The term supposedly emphasizes that data graphs are stored as they are posted and requested by simple webapps (as opposed to normalized relational data), but that still hasn't anything to do with documents as understood by most people. It just poisons the search space (and AWS calling their impl DocumentDB doesn't help either).
