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On Tue, 2008-10-14 at 15:57 -0400, rob@xxxxxxxxx wrote:
One - I don't see this as too tricky:
if %nullind(termDate);
dsply 'employee is active';
else;
dsply 'employee was terminated ' + %char(termDate);
endIf;
or any more lines of code than
if termDate = MichelangelosBirthday;
dsply 'employee is active';
else;
dsply 'employee was terminated ' + %char(termDate);
endIf;

I am indeed an old guy, but I think my distaste for null-capable fields
is an orthogonal attribute <grin />.

If Fld1 is a null capable character field, the each expression testing
the field must be prepared to deal with the counter-intuitive
possibility that the expressions
Fld1 = 'X'
and
Fld1 <> 'X'
are both false. Indeed, you cannot even assert that
Fld1 = Fld1
. Who needs the hassle?

(Yes, I am prepared to defend the thesis that Laziness Is A Virtue!)


You do have some leg to stand on that if an incompetent programmer were to
check termDate without checking it's null indicator they can get into
trouble. For example if I do
termDate = date(); // set to current date
%nullind(termDate) = *on; // set termDate off as employee is active
dsply termDate; // even though null, it will still display today's date
But, who's to say that same programmer wouldn't figure that a date of
0001-01-01 or Michelangelo's Birthday or whatever wasn't a valid date?

Were you hoping that IBM had written the compiler so that if you tried
dsply termDate;
and if termDate was null then you'd get a messy MCH type message as if you
tried to dsply a variable that wasn't passed into the program and you
failed to check %addr on that?

That sounds good to me.


Eric Delong's suggestion to "propogate nullness" also makes
sense, and it has parallels in for example ...

(*) The Memcheck tool in
Valgrind (<http://en.wikipedia.org/wiki/Valgrind>,
<http://valgrind.org/>), which propogates an "is initialized"
attribute throughout the execution of a propram.

(*) perl taint mode
(<http://gunther.web66.com/FAQS/taintmode.html>), which
propogates "is untrusted input" throughout execution of a
program.

But to do anything like this requires a concept of "variable"
entirely different the traditional concept of an RPG variable.


Cheers,
Terry.

I take it you also have an issue with
select termDate
into :termDate :termDateInd
from ....


Rob Berendt
--
Group Dekko Services, LLC
Dept 01.073
Dock 108
6928N 400E
Kendallville, IN 46755
http://www.dekko.com





"DeLong, Eric" <EDeLong@xxxxxxxxxxxxxxx>
Sent by: midrange-l-bounces@xxxxxxxxxxxx
10/14/2008 03:04 PM
Please respond to
Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxx>


To
"Midrange Systems Technical Discussion" <midrange-l@xxxxxxxxxxxx>
cc

Subject
RE: Interesting question and debate on ddl tables with date fieldsthatwill
not always have a value






So, are you saying that you use null support for all your business
applications? From the perspective of your users, would they ever be
able to tell the difference between an application using null support,
and an application using legacy techniques?

Seriously, my gripe is not the concept of null value, or even how SQL
processes in the presence of null values, but is about how hard (messy)
it is in a HLL like RPG. The reality is, if you MUST support null
capable fields in RPG, you must ALWAYS check the null indicator before
you EVER access the field in question. Did you know that even a null
field will still return a valid value during a fetch? It might be the
default initial value for that data type, or it might contain some other
value (assuming the field was set to null AFTER it had a value stored).


If IBM made null support more transparent, I would probably recommend it
usage. As it is, I don't think most developers would be disciplined
enough to always use it properly.

JMO,
Eric DeLong

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Walden H. Leverich
Sent: Tuesday, October 14, 2008 1:02 PM
To: Midrange Systems Technical Discussion
Subject: RE: Interesting question and debate on ddl tables with date
fieldsthatwill not always have a value

Use nulls, that's what they're for!

Not to make this an state-of-the-nation discussion, but it's the very
fact that many people aren't willing to use the "current" stuff, that
makes an i look old. Imagine this question from an outsiders point of
view... the rest of the world uses null, to a SQL Server programmer this
wouldn't even be a question. Looking at an i, we'd see that we "can't"
use nulls, so i must be old! Granted, it's not that the i can't handle
them technically, but that our programmers can't handle them. Well,
sooner or later the programmers have to upgrade their skills, or guess
what, the machine IS old.

-Walden

--
Walden H Leverich III
Tech Software
(516) 627-3800 x3051
WaldenL@xxxxxxxxxxxxxxx
http://www.TechSoftInc.com

Quiquid latine dictum sit altum viditur.
(Whatever is said in Latin seems profound.)


-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Doug Palme
Sent: Tuesday, October 14, 2008 12:06 PM
To: Midrange Systems Technical Discussion
Subject: Interesting question and debate on ddl tables with date fields
thatwill not always have a value

I hope that subject description makes it clear. We are having an
internal
debate and discussion as we make the move towards sql tables and ddl
files; specifically using date data types.

An example, an employee file has two dates, HireDate and TermDate,
self
explanatory.....one is when the person is hired and the other is when
they
leave.

Obviously while they are an employee, they do not have a term date,
so how
do we handle that?

suggestions? comments? thoughts?

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