From: Logan Capaldo <logancapaldo@...>
Date: 2006-03-05T11:00:20+09:00
Subject: Re: Kirbybase Hacks NilClass

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On Mar 4, 2006, at 6:07 PM, angus wrote:

> But doesn't NULL always propagate in "database semantics"? I mean,  
> if any
> subexpression is NULL, the whole expression becomes NULL. It's the  
> expected
> behaviour (but maybe not to the users of KirbyBase). In SQL,  
> normally, one
> uses NVL(a, b) (with the meaning 'a.nil? ? b : a') to guard  
> subexpressions
> against NULL.

Well based on my intro to db class SQL uses a three-way boolean logic

NULL or TRUE = TRUE
NULL or FALSE = FALSE

NULL and TRUE =  NULL
NULL and FALSE = FALSE

not NULL = NULL

Boolean ops involving only TRUE and FALSE work as usual
  
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