Posted by Ed Murphy on 03/30/07 01:08

--CELKO-- wrote:

> All data types have to be NULL-able in SQL. Having a BOOLEAN type
> would lead to 4 valued logic with inconsistent rules about how NULLs
> propagate. And the various vendor extension do not work or port
> either.

It seems like dropping UNKNOWN would leave a sensible set of rules:

and | T N F or | T N F not |
----+------ ---+------ ----+--
T | T N F T | T T T T | F
N | N N F N | T N N N | N
F | F F F F | T N F F | T

Am I overlooking anything?

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