Re: Question on Structuring Product Attributes

On Sat, 9 Feb 2013 16:34:51 -0800 (PST)
derek.asirvadem_at_gmail.com wrote:

> ? NULL equals NULL

Well, for operator AND, Kleene and Lukaeiwicz say

	T T T
	T F F
	T U U
	F T F
	F F T
	F U U
	U T U
	U F U
	U U F  <== you're saying U U T

Could you please tell me which 3VL supports your contention that NULL = NULL?
> No. SELECT does not require a FROM. The mandate of the RM is higher
> than the vendor-mandate of the SQL Committee.

Lennart said, reasonably, that SELECT is the SQL version of RM RESTRICT. If there's no FROM, there's logically nothing to restrict, ergo "select 1" should return no row (not 1 and not NULL).

You could argue that

        select 1

is short for an implicit row constructor, e.g,

        select 1 from ( VALUES( 'foo' ) ) as T

but you didn't. I might, but then I'm not sure why SQL requires SELECT when there's no project required. IMO

        VALUES(1) would serve as well or better.

> SQL is data sublanguage defined in the RM; it is the servant of the
> RM, not the other way around.

If only. AFAIK the word "relational" doesn't appear in the SQL standard unless to explicitly deny fealty to it. Received on Mon Feb 11 2013 - 01:38:54 CET