The application still has foreign key references and JOIN, which you don't get in a k/v store, you just don't have the actual CONSTRAINT. MySQL worked this way

The application still has foreign key references and JOIN, which you don't get in a k/v store, you just don't have the actual CONSTRAINT. MySQL worked this way for literally decades with the MyISAM storage engine that does not have referential integrity constraints, it just allows the FOREIGN KEY syntax to pass silently.