It's noteworthy that SQL's 3VL follows Kleene's K3 logic (or, equivalently, Łukasiewicz' Ł3 logic) and not Priest's P3 logic. That is, in K3 and Ł3, an unknown

It's noteworthy that SQL's 3VL follows Kleene's K3 logic (or, equivalently, Łukasiewicz' Ł3 logic) and not Priest's P3 logic. That is, in K3 and Ł3, an unknown (or indeterminate/null) value resolves to neither true nor false; whereas in K3, an unknown (or indeterminate/null) value resolves to both true and false. There are some interesting ramifications of these properties, including a lack of tautologies in K3 and Ł3.