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

In article <1134354197.583597.21280_at_o13g2000cwo.googlegroups.com>, boston103_at_hotmail.com says...
>
> Hugo Kornelis wrote:
>
> > There is a reson to object to the use of "the null value" to represent
> > the truth value Unknown. Elsewhere in the standard, the Null value is
> > defined as "A special value that is used to indicate the absence of any
> > data value". Of course, if Unknown is considered to be a data value for
> > a boolean data type (and the rest of the standard clearly indicates it
> > is), it should not be represented by the same symbol that is also used
> > to represent the absence of a data value, since a data value can not be
> > absent and present at the same time.
>
> Right.
>
> > Further in the document, in the part where <boolean value expression> is
> > detailed, the boolean truth tables are given. According to these tables,
> > False AND Unknown should evaluate to False and True OR Unknown should
> > evaluate to True. Makes sense. But since Unknown and NULL are considered
> > equal in the context of a Boolean data type, this also means that False
> > AND NULL evaluates to False and True OR NULL evaluates to True. The
> > basic rule of NULL propagation is out of the window!!
>
> Apparently, whoever created this part of the standard had no clue
> about what any kind of logic is.

Or perhaps they thought it was not a problem at all to use the same word "NULL" for different concepts, behaving differently. After all, it is obvious from the context when NULL means 'missing' and when it means 'unknown', no? :)

-- 
Jon