It is a declarative language. But the underlying math of SQL is that of relations. It's closer to prolog than to Haskell. I don't know much about the theory of

It is a declarative language. But the underlying math of SQL is that of relations. It's closer to prolog than to Haskell. I don't know much about the theory of SQL but at least I can draw on the analogy of deriving algorithms in a Relational setting vs a functional to emphasize that the essence of functions is not the same as the essence of relations: Unlike functions, relations can be nondeterministic and each relation has a converse.