RE: Months are weird, was '3 Months Ago?'

Birgitta,

The v5r4 reference manual makes no mention of an Add_Months() function.

Was it PTF'd in?

Charles

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of BirgittaHauser
Sent: Thursday, May 17, 2007 10:12 AM
To: 'RPG programming on the AS400 / iSeries'
Subject: AW: Months are weird, was '3 Months Ago?'

Hi,

If you want to guarantee, that adding or substracting a
number of months to the month's end will also result in a
month end and if you are already on release V5R4, you can use
the SQL scalar function Add_Months.

Example:
D MyStartDate S D
D MyEndDate S D
*******************************************************************
/Free
MyStartDate = D'2007-05-31';
Exec SQL Set :MyEndDate = Add_Months(:MyStartDate, -3);
Dsply MyEndDate; //--> '2007-02-28'

Exec SQL Set :MyEndDate = Add_Months(:MyEndDate, 3);
Dsply MyEndDate; //--> '2007-05-31'

MyStartDate = D'2007-04-30';
Exec SQL Set :MyEndDate = Add_Months(:MyStartDate, -3);
Dsply MyEndDate; //--> '2007-01-31'

Exec SQL Set :MyEndDate = Add_Months(:MyEndDate, 3);
Dsply MyEndDate; //--> '2007-04-30'

*InLR = *On;
/End-Free


Mit freundlichen Grüßen / Best regards

Birgitta Hauser

"Shoot for the moon, even if you miss, you'll land among the
stars." (Les
Brown)
"If you think education is expensive, try ignorance." (Derek
Bok) "What is worse than training your staff and losing them?
Not training them and keeping them!"

-----Ursprüngliche Nachricht-----
Von: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] Im Auftrag von
AGlauser@xxxxxxxxxxxx
Gesendet: Thursday, May 17, 2007 15:59
An: RPG programming on the AS400 / iSeries
Betreff: Re: Months are weird, was '3 Months Ago?'


Booth Martin wrote on 17/05/2007 09:39:50:

What bothers me is that dates don't round trip well. Does

March 31st

less one month, plus one month, equal March 31st?

It bothers me too, but I'm not sure there would be a sensible
way to implement month arithmetic so that March 31 could
round trip. Suppose that

a = 2007-03-31
b = a - 1 month + 1 month

If b = a, then you would just have another inconsistency.

c = a - 1 month
d = 2007-02-28

I think that we can agree that c = d. But then you have

c + 1 month = d + 1 month
(a - 1 month) + 1 month = (2007-02-28) + 1 month
2007-03-31 = 2007-02-28
.........................
uh-oh!

Dates arithmetic will never behave like integer arithmetic,
because 'months' and 'years' are not really consistently defined.

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