Re: NULLs: theoretical problems?

On Wed, 08 Aug 2007 20:42:52 GMT, paul c wrote:

>Hugo Kornelis wrote:
>> ...
>> The ANSI standard defines NULL as follows:
>>
>> "null value: A special value that is used to indicate the
>> absence of any data value."
>>
>> Thus, the only concept collapsed into NULL is that of "no value here".
>> ...
>
>Thanks for a great quote. The notion that that there is a value that
>conveys that the value is not a value suggests that the SQL committee
>has its fair share of mystics, too. Either that, or they are not
>required to read what they write.

Hi Paul,

<nitpicking>
The ANSI text doesn't define "the null value" (as they call it) as a value that conveys that the value is not _a_ value, but as a _special_ value that conveys that there is no _data_ value. </nitpicking>

Personally, I never call NULL a value, and I prefer to describe NULL as a "marker that indicates the absence of any value". But I couldn't really write that and still claim to be citing ANSI, eh?

>Another paradox is the db that is based only on values, except when it's
>not.

IMO, a db is not based on values but on predicates. Combinations of two or more columns from a single table can be read as sentences, with the fixed part of the sentence implied by the schema and the design documents, and the variable part of the sentence filled in with the values in the columns.

Best, Hugo Received on Thu Aug 09 2007 - 00:16:30 CEST