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BUG #13845: Incorrect week number

kees.westerlaken@valuecare.nl

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From: kees.westerlaken@valuecare.nl
To: pgsql-bugs@postgresql.org
Date: 2016-01-05T10:59:24Z
Lists: pgsql-bugs 
The following bug has been logged on the website:

Bug reference:      13845
Logged by:          Kees Westerlaken
Email address:      kees.westerlaken@valuecare.nl
PostgreSQL version: 9.2.10
Operating system:   Linux
Description:        

2016 is a year where week numbers (US) differ from ISO.

On 1 januari 2016 it works OK.
select to_char(to_date('20160101', 'YYYYMMDD'), 'YYYYWW')
produces 201601, while 
select to_char(to_date('20160101', 'YYYYMMDD'), 'YYYYIW')
produces 201553.

However on 4 januari 2016
select to_char(to_date('20160104', 'YYYYMMDD'), 'YYYYWW')
produces 201601, which should be 201602 !!

And surprisingly on 8 januari 2016, which is in the same week as 4 januari
select to_char(to_date('20160108', 'YYYYMMDD'), 'YYYYWW')
produces 201602, which is correct.