Nati Shalom uses the old CS saying “Any software problem can be solved by adding another layer of indirection” to suggest that NoSQL databases could support SQL queries (and not only):
The key is the decoupling of the query semantics from the underlying data-store as illustrated in the diagram below:
While it’s difficult to strongly argue against it, the real question is: how difficult will be for such a layer to calculate the costs of such queries? Or differently put:
The two software problems that can never be solved by adding another layer of indirection are that of providing adequate performance or minimal resource usage.
— Jeff Kesselman