Re: 3 value logic. Why is SQL so special?
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Tue, 19 Sep 2006 12:16:14 GMT
Message-ID: <icRPg.22832$9u.272599_at_ursa-nb00s0.nbnet.nb.ca>
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> All these arguments against NULL are only valid against some specific
> implementations of that concept - here SQL in its various dialects.
> They are not arguments against the concept of having null-values (e.g.
> to represent unknown values) in some database system. And this is
> comp.databases.theory after all.
Date: Tue, 19 Sep 2006 12:16:14 GMT
Message-ID: <icRPg.22832$9u.272599_at_ursa-nb00s0.nbnet.nb.ca>
peter koch wrote:
>>Chris Lim wrote: >> >> >>>Roy Hann wrote:
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>>Then why have I had to spend so much time in my career explaining to >>reasonably intelligent people why their queries returned the wrong answer?
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>>I must insist you back up that statement quantitatively and >>qualitatively. It is far easier to deal with two names than with >>surprisingly inconsistent semantics for the same reason it is far easier >>to deal with a compile-time error than a run-time error.
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>> But a >> >>>database without NULLs? It might be theorectically correct, but it >>>would be a nightmare to write queries against. >> >>I disagree. My personal experience dealing with scores of intelligent >>database users suggests that NULL is the nightmare.
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> All these arguments against NULL are only valid against some specific
> implementations of that concept - here SQL in its various dialects.
> They are not arguments against the concept of having null-values (e.g.
> to represent unknown values) in some database system. And this is
> comp.databases.theory after all.
I have found the arguments against 3VL and NVL for N > 2 compelling. For example, if DEE and DUM are canonical relations for true and false, what are the canonical relations for the other logical values?
The whole point of NULL is to have something other than a value to represent missing information. To use a value to represent unknown, what we really need are extensible data type systems that as much as possible enforce consistency. For example, if SUM is an aggregate of +, an extensible data type system should enforce consistent semantics + semantics for SUM. Received on Tue Sep 19 2006 - 14:16:14 CEST