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Re: So what's null then if it's not nothing?

From: vc <boston103_at_hotmail.com>
Date: 28 Nov 2005 19:37:19 -0800
Message-ID: <1133235439.911174.269240@o13g2000cwo.googlegroups.com>

michael_at_preece.net wrote:
[...]

> NULL, as defined in mathematics and according to the root meaning for
> the word in the dictionary, is, properly, an empty set

Forget the dictionary. Please give the reference to a/the book where we can find "NULL, as defined in mathematics [..] is, properly, an empty set". What kind of "mathematics" is it that defines NULL as an empty set ?

>There is no 3VL with
> this NULL.
>There is no distinction between two NULL values. Things are
> either distinct or not distinct - never unknown.
>

SQL'92 standard most certainly treats NULL as a 3VL symbol (forgetting for a moment about some SQL inconsistencies ). The standard does so, rightly or wrongly, following Codd's work in this area. See, for example, "Extending the relational model to capture more meaning", 1979.

A lot of confusion about NULL stems from the fact that it's unclear what NULL really means. Codd mentions two meaning: "value at present unknown" and "property inapplicable." In his later work,  he introduced a 4VL based on the different kinds of nulls. Some researchers suggested even more possible meanings for NULL.

> If you (SQL) need a special value for this then use
> something else - use "UNKNOWN" or whatever you like, but don't corrupt
> NULL.
The "corruption" exists only in your imagination since, firstly, NULL use in SQL is based on 25 year-old Codd's work in the area and it's hardly fair to make practitioners abandon the well established terminology. Secondly, you've failed to provide the pristine NULL definition that one could measure the SQL impure NULL against, ;)

>
> Mike.
Received on Mon Nov 28 2005 - 21:37:19 CST

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