Re: NULLs: theoretical problems?

Jan Hidders <hidders_at_gmail.com> wrote in news:1187811230.504947.11400_at_x40g2000prg.googlegroups.com:

> On 22 aug, 17:37, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:

>> In your language,  the expression 'def y:x AND y' where 'y' is
>> 'undefined' evaluates to 'false'.  In SQL, the expression 'x AND y'
>> where 'y'is 'unknown' evaluates to 'unknown'.  The effect of having a
>> predicate that evaluates to 'unknown' is the same as having a
>> predicate that evaluates to 'false':  no rows will be selected. 
>> That's what I meant by "substituting 'false' for unknown".

I am not sure I understand what you mean by "That's not exactly the same...", but I'll take a stab at it.

If "the same" comes from "The effect of having a predicate that evaluates to 'unknown' is the same as having a predicate that evaluates to 'false'", then "there are formulas f(x) that evaluate to 'true' if x is 'unknown'", although true, is not relevant really, in which case "That's not exactly the same..." is not substantiated. I've never said that any formula f(x) where x is unknown evaluates to false !

Why don't we try and bring more precision into what we are saying? I do not find verbal games very interesting !

> -- Jan Hidders
>
>
Received on Thu Aug 23 2007 - 00:13:03 CEST