RE: null capable fields

Joep,
There is a bit of confusion floating about as to how NULL works.  One cannot
set the value of VAR to NULL.  The value of VAR is independent of the null
indicator.  One can set the value of VAR to 10 and also set the null
indicator to NULL.  In effect, VAR would be NULL and 10 at the same time.
It's up to your program to test for the NULL indicator separately from
testing the value of the variable.

As you said, this can lead to some interesting IF THEN ELSE constructs, but
usually, a test for NULL precedes (and supercedes) the value comparisons, so
it's more like a CASE then a complex IF THEN clause.

Buck Calabro
Aptis; Albany, NY
mailto:Buck.Calabro@aptissoftware.com

> -----Original Message-----
> From: Joep Beckeringh 
> Sent: Wednesday, September 08, 1999 7:01 PM
> To:   RPG400-L@midrange.com
> Subject:      Re: null capable fields
> 
> ----- Oorspronkelijk bericht -----
> Van: McCallion, Martin <MccalliM@Midas-Kapiti.com>
> 
>  <snip>
> > Oh.  Thanks.  I thought it must be much more complex than that.
>  <snip>
> 
> Oh, but it is, as soon as you get into boolean logic.  Normally, the
> expression 'var > 10' is easily understood.  It is TRUE for all values of
> var greater than 10 and FALSE for 10 and lower.  But what if var is NULL?
> Is the expression TRUE, FALSE or maybe something like UNDEFINED or NULL?
> And if it is FALSE, does that mean that the opposite, 'var <= 10' is TRUE?
> Leads to some interesting IF - THEN - ELSE constructs, especially if you
> combine some expressions.
> 
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