RE: Week Number Coding

Ok, WEEK_ISO works pretty good.  However if you plan on doing something
like passing a date and getting YYW## where yy=year and ##=week number then
you better be careful.  If Month of that date is 01 and the week >6 then
subtract 1 from the year.  For example 2000-01-01=1999-W52-6.

Gee, don't you think another few date formats are needed to support week
notation with/without separators and with/without the day of the week?

Copying from:
http://www.cl.cam.ac.uk/~mgk25/iso-time.html

In commercial and industrial applications (delivery times, production
plans, etc.), especially in Europe, it is often required to refer to a week
of a year. Week 01 of a year is per definition the first week that has the
Thursday in this year, which is equivalent to the week that contains the
fourth day of January. In other words, the first week of a new year is the
week that has the majority of its days in the new year. Week 01 might also
contain days from the previous year and the week before week 01 of a year
is the last week (52 or 53) of the previous year even if it contains days
from the new year. A week starts with Monday (day 1) and ends with Sunday
(day 7). For example, the first week of the year 1997 lasts from 1996-12-30
to 1997-01-05 and can be written in standard notation as

1997-W01 or 1997W01

The week notation can also be extended by a number indicating the day of
the week. For example, the day 1996-12-31, which is the Tuesday (day 2) of
the first week of 1997, can also be written as

1997-W01-2 or 1997W012

for applications like industrial planning where many things like shift
rotations are organized per week and knowing the week number and the day of
the week is more handy than knowing the day of the month.

An abbreviated version of the year and week number like

95W05


Rob Berendt
--
"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety."
Benjamin Franklin


select mydate,week_iso(mydate)
from rob/a7
will return:
MYDATE    WEEK_ISO ( MYDATE )
01/01/00                52
01/02/00                52
01/03/00                 1
01/04/00                 1
01/01/02                 1
01/07/02                 2
01/06/02                 1


select mydate,week(mydate)
from rob/a7
will return:
MYDATE    WEEK ( MYDATE )
01/01/00               1
01/02/00               2
01/03/00               2
01/04/00               2
01/01/02               1
01/06/02               2
01/07/02               2

Two problems:
1)  01/01/00 was on a Saturday.  Thus the first week began with Monday
01/03/00.
2)  Sunday's are the last day of a week, not the first.