In the relational model used by SQL, types are atomic. Sum types are inherently non-atomic. I'm sure you could graft them onto the language, the same way Postgr

In the relational model used by SQL, types are atomic. Sum types are inherently non-atomic. I'm sure you could graft them onto the language, the same way Postgres can have JSON type fields and all that, but I don't think you'd be able to really integrate them into SQL without fundamentally changing what kind of language SQL is.