Re: 3 value logic. Why is SQL so special?
From: Volker Hetzer <firstname.lastname_at_ieee.org>
Date: Mon, 18 Sep 2006 17:21:39 +0200
Message-ID: <eemdi3$1t3$1_at_nntp.fujitsu-siemens.com>
>
> In a database without NULLs, would you have to do LEFT OUTER JOINs in
> all queries where you want all rows from your 'main' table returned,
> regardless of whether they have the optional attributes or not? Say,
> for example, all flights, with or without an actual departure time. And
> if so, how do the 'missing' attributes get returned from these queries,
> if NULLs are not allowed?
Besides, wasn't there a rule that the result of a relational operation should be a table too?
Therefore an "insert into xxx select ... from ..." should always work. Voila, there are the nulls in xxx.
What I don't understand is that everyone who decries nulls, somewhere works with default values. Ok, big deal, NULL is an universally applicable default value that cannot be confused with real data. What am I missing?
Btw, what would be the consequences of NULL=NULL being true?
Date: Mon, 18 Sep 2006 17:21:39 +0200
Message-ID: <eemdi3$1t3$1_at_nntp.fujitsu-siemens.com>
Chris Lim schrieb:
> Cimode wrote:
>> And many other information... >> This is a purely pedagogical case (far from being complete) to >> demonstrate that it is perfectly possible to build some logical design >> in minutes (took me 20 of them) WITHOUT using NULLS...while sticking to >> the God Damn Real World (lazyness) excuse...
>
> In a database without NULLs, would you have to do LEFT OUTER JOINs in
> all queries where you want all rows from your 'main' table returned,
> regardless of whether they have the optional attributes or not? Say,
> for example, all flights, with or without an actual departure time. And
> if so, how do the 'missing' attributes get returned from these queries,
> if NULLs are not allowed?
Besides, wasn't there a rule that the result of a relational operation should be a table too?
Therefore an "insert into xxx select ... from ..." should always work. Voila, there are the nulls in xxx.
What I don't understand is that everyone who decries nulls, somewhere works with default values. Ok, big deal, NULL is an universally applicable default value that cannot be confused with real data. What am I missing?
Btw, what would be the consequences of NULL=NULL being true?
Lots of Greetings!
Volker
-- For email replies, please substitute the obvious.Received on Mon Sep 18 2006 - 17:21:39 CEST