What you're talking about requires compound data types in the first place (e.g., lists in your example), whereas in the relational model, attributes are normall

What you're talking about requires compound data types in the first place (e.g., lists in your example), whereas in the relational model, attributes are normally assumed to range over primitive types. But, even in the absence of compound data types, the answer to a Prolog query may contain free variable, whereas the answer to SQL query may not. So you do have a point.