There's a difference if the client developers can register stored procedures. Typically, you can't do that with RPC, and it's a big value-add of GraphQL.

If that happens, then SQL and GraphQL look a lot alike. SQL would be more powerful, which also means that it'd probably be somewhat harder to implement, though there are so many SQL engines existing. I can't imagine people implementing from scratch.

I can't wait for Hasura SQL-to-GraphQL-to-SQL.