The inventors of GraphQL did not intend it to be mapped directly to a database.
"That would be one way to implement the system in a DB-centric way. However we believe that intermediate application code is pretty critical to any GraphQL implementation." [1]
"GraphQL is a client-server dance that needs server-side capabilities, not just CRUD semantics." [2]
Specifically, GQL implementations always map to a `resolve(source, args, context, info)` function (the names can be anything, the types are what matter). In that sense, you also get a standard server interface similar to wsgi/psgi/rack, but much more fine-grained (there can be a resolver for every field in the query).
GQL implementations don't map to the database but to application code.