Oreilly - Nulls, Three-Valued Logic, and Missing Information by C.J. Date | Publisher: O'Reilly Media,...
The logic on which the relational model is based is a two valued logic (2VL). In its attempt to deal with the so called “missing information” problem, however, SQL—more specifically, SQL's support for “nulls”—is based on a three valued logic (3VL) instead. This session explains in detail why any such...