The logic of three-valued logic

re: The logic of three-valued logic

James Luetkehoelter — Wed, 18 Jul 2007 09:28:43 GMT

Beautifully done. This is a great discussion of three-valued logic. How about tackling Belief Logic and SSAS Data Mining :)

re: The logic of three-valued logic

David Portas — Sat, 21 Jul 2007 11:28:32 GMT

Good information Hugo. The only danger is that by trying to relate three-value logic to everyday examples of what we know and don't know someone might infer that the truth value "unknown" is directly related to its usual meaning in English. You gave one example where that isn't the case: "WHERE Age > 35 AND Age < 30". An even simpler example would be "WHERE Age = Age". Again, we don't have to know your age to know that the value of Age is equal to itself. The value of this predicate is not unknown in mathematical terms or in everyday experience. So it would be safer and less counter-intuitive if SQL named the third truth value as something else altogether - the common English meaning of the word "unknown" clearly does not apply.

re: The logic of three-valued logic

Hugo Kornelis — Sat, 22 Sep 2007 10:06:57 GMT

Note to all - while rereading this post in preparation of the third part of this series (do I hear someone say "at last"?), I noted a disturbing error.

In the second paragraph after the heading "CHECK, the odd one out" I had mistakenly types WHERE instead of WHILE. Not once but twice. Aaarrgghh!!!

Since this is not just an amusing type, but actually an error that changes what I want to say, I just went in and corrected my mistake. If my error has confused you, then please know that I am sorry, and accept my apologies.

Dr. Unknown, or how I learned to stop worrying and love the NULL

SELECT Hints, Tips, Tricks FROM Hugo Kornelis WHERE RDBMS = 'SQL Server' — Sat, 22 Sep 2007 20:35:06 GMT

Two months ago, I posted the first two parts of a series about NULL. After that, I went quiet. Much to

re: The logic of three-valued logic

Hugo Kornelis — Mon, 01 Oct 2007 06:17:28 GMT

The fourth (and final) part of this series about NULL is now available at http://sqlblog.com/blogs/hugo_kornelis/archive/2007/09/30/what-if-null-if-null-is-null-null-null-is-null.aspx.

The Sad State Of Programmers Part 2 : The In Person Interview

Denis Gobo — Mon, 10 Dec 2007 20:02:12 GMT

This is part two of a three part series. Part one was about the phone interview , this part is about