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Published on Jun 19, 2012
Date describes the three-valued logic approach to missing information ("nulls") in depth. Both the underlying theory and SQL's attempt to implement that theory will be described. In particular, Date will show why the approach is a disastrously bad one and will sketch an alternative and logically sounder approach. Topic outline: Types of null UNK, unk, and three-valued logic (3VL) Consequences of the 3VL approach SQL's implementation of 3VL Outer join Further thoughts So what can we do?