Oracle week calculation issue
I am using Oracle's to_char() function to convert a date to a week number (1-53):
select pat_id,
pat_enc_csn_id,
contact_date,
to_char(contact_date,'ww') week,
...
the 'ww' switch gives me these values for dates in 开发者_StackOverflow社区January of this year:
Date Week
1-Jan-10 1
2-Jan-10 1
3-Jan-10 1
4-Jan-10 1
5-Jan-10 1
6-Jan-10 1
7-Jan-10 1
8-Jan-10 2
9-Jan-10 2
10-Jan-10 2
11-Jan-10 2
12-Jan-10 2
a quick look at the calendar indicates that these values should be:
Date Week
1-Jan-10 1
2-Jan-10 1
3-Jan-10 2
4-Jan-10 2
5-Jan-10 2
6-Jan-10 2
7-Jan-10 2
8-Jan-10 2
9-Jan-10 2
10-Jan-10 3
11-Jan-10 3
12-Jan-10 3
if I use the 'iw' switch instead of 'ww', the outcome is less desirable:
Date Week
1-Jan-10 53
2-Jan-10 53
3-Jan-10 53
4-Jan-10 1
5-Jan-10 1
6-Jan-10 1
7-Jan-10 1
8-Jan-10 1
9-Jan-10 1
10-Jan-10 1
11-Jan-10 2
12-Jan-10 2
Is there another Oracle function that will calculate weeks as I would expect or do I need to write my own?
EDIT
I'm trying to match the logic used by Crystal Reports. Each full week starts on a Sunday; the first week of the year starts on whichever day is represented by January 1st (e.g. in 2010, January 1st is a Friday).
When using IW, Oracle follows the ISO 8601 standard regarding week numbers (see http://en.wikipedia.org/wiki/ISO_8601). That is the same standard than the one we generally use in Europe here.
Your problem is also mentioned on the Oracle forum: http://forums.oracle.com/forums/thread.jspa?threadID=947291 and http://forums.oracle.com/forums/message.jspa?messageID=3318715#3318715. Maybe you can find a solution there.
I know this is old, but still a common question.
This should give you the correct results in the smallest amount of effort:
select pat_id,
pat_enc_csn_id,
contact_date,
to_char(contact_date + 1,'IW') week,
...
Since it looks like you are using your own special definition of the week number you'll need to write your own function.
It might be helpful that NLS_TERRITORY affects the day with which a week starts as used by the D Format Model
see also:
http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/sql_elements004.htm#SQLRF00210
and
http://www.adp-gmbh.ch/ora/sql/to_char.html
Based on this question, How do I calculate the week number given a date?, I wrote the following Oracle logic:
CASE
--if [date field]'s day-of-week (e.g. Monday) is earlier than 1/1/YYYY's day-of-week
WHEN to_char(to_date('01/01/' || to_char([date field],'YYYY'),'mm/dd/yyyy'), 'D') - to_char([date field], 'D') > 1 THEN
--adjust the week
trunc(to_char([date field], 'DDD') / 7) + 1 + 1 --'+ 1 + 1' used for clarity
ELSE trunc(to_char([date field], 'DDD') / 7) + 1
END calendar_week
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