Re: ISO Week of Year

From: Maxim Demenko <mdemenko_at_gmail.com>
Date: Wed, 21 Jan 2009 01:01:02 +0100
Message-ID: <497665BE.3000707_at_gmail.com>

Geoff Muldoon schrieb:
> Hi all,
>
> Oracle 10.2.0.3 on Linux ...
>
> I'm having difficulty with a proc which tries to compare data across years
> at a specific point in time.
>
> For a particular input_date and comparison_year, I'm trying to retrieve a
> comparison_date based on the day-of-week of the input_date and the
> corresponding ISO-week-of-year.
>
> EG:
> input_date 08-jan-2009 (Thursday, ISO-week-of-year 2) and comparison_year
> 2007, I'll get a result of 11-jan-2007 (the Thursday of ISO-week-of-year 2
> in that year).
>
> I realise that I have now to deal with where there is no matching date,
> for example where the input_date's year might have 53 ISO-weeks and the
> comparison_year only 52.
>
> The problem I'm having is working out when ISO-week-of years actually
> start.
>
> select to_char(to_date('01-jan-1998', 'dd-mon-yyyy'), 'IW')
> from dual -- this is a Thursday
> --
> 01
>
> select to_char(to_date('01-jan-1999', 'dd-mon-yyyy'), 'IW')
> from dual -- this is a Friday
> --
> 53
>
> Can anyone help in explaining this?
>
> Geoff M

Does that help?
http://www.phys.uu.nl/~vgent/calendar/isocalendar.htm

Best regards

Maxim Received on Tue Jan 20 2009 - 18:01:02 CST