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A Simple Formula to Calculate the ISO Week Number


A Simple Formula to Calculate the ISO Week Number

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SwePeso
SwePeso
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Yes, I did indeed. However, the time at my place was 3 am and time to go to bed...

Here is a further reduced code (one less addition)
(DATEPART(DAYOFYEAR, DATEADD(DAY, DATEDIFF(DAY, '17530101', @Date) / 7 * 7, '17530104')) + 6) / 7



My blog about this is here.
If you don't read Swedish well, use either Bing or Google.


N 56°04'39.16"
E 12°55'05.25"
Jeff Moden
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SwePeso (7/27/2013)
Yes, I did indeed. However, the time at my place was 3 am and time to go to bed...

Here is a further reduced code (one less addition)
(DATEPART(DAYOFYEAR, DATEADD(DAY, DATEDIFF(DAY, '17530101', @Date) / 7 * 7, '17530104')) + 6) / 7



My blog about this is here.
If you don't read Swedish well, use either Bing or Google.


Thanks, Peter. I'll check out the formula.

My question was based on the fact that we weren't receiving each other's emails in the past.

--Jeff Moden

RBAR is pronounced ree-bar and is a Modenism for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
     Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column.
Although they tell us that they want it real bad, our primary goal is to ensure that we dont actually give it to them that way.
Although change is inevitable, change for the better is not.
Just because you can do something in PowerShell, doesnt mean you should. Wink

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robert.sterbal 56890
robert.sterbal 56890
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Now what happens when a government decides to skip a day...
Jeff Moden
Jeff Moden
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robert.sterbal 56890 (10/23/2015)
Now what happens when a government decides to skip a day...


Then it's no longer "ISO". ;-)

What's your real question?

--Jeff Moden

RBAR is pronounced ree-bar and is a Modenism for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
     Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column.
Although they tell us that they want it real bad, our primary goal is to ensure that we dont actually give it to them that way.
Although change is inevitable, change for the better is not.
Just because you can do something in PowerShell, doesnt mean you should. Wink

Helpful Links:
How to post code problems
How to post performance problems
Forum FAQs
robert.sterbal 56890
robert.sterbal 56890
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I like the way your formula skips the leap year problem.

I still remember when the church moved the calendar by a couple of weeks - https://en.wikipedia.org/wiki/Gregorian_calendar
ChrisM@Work
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robert.sterbal 56890 (10/23/2015)
...
I still remember when the church moved the calendar by a couple of weeks - https://en.wikipedia.org/wiki/Gregorian_calendar



Jeff - there's someone older than you on ssc ;-)

“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw

For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden
Exploring Recursive CTEs by Example Dwain Camps
robert.sterbal 56890
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ChrisM@Work (10/23/2015)
robert.sterbal 56890 (10/23/2015)
...
I still remember when the church moved the calendar by a couple of weeks - https://en.wikipedia.org/wiki/Gregorian_calendar



Jeff - there's someone older than you on ssc ;-)



I may or may not be older, but Jeff is definitely wiser and smarter!
Beugen
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Hi

Thanks for this simple and effective code.
Is there a similar easy way to get the year of that week we are looking for? Or the "ISO-year"?

Lets say I put in the date '2014-12-31' and get the ISO-WeekNumber = 1, I would also like to get the what year that weeknumber is for (in this case 2015).
I guess I can try to find this out, but if you guys already have some really efficient code to do this, it would be appreciated.

br
Gert
Jeff Moden
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robert.sterbal 56890 (10/23/2015)
I like the way your formula skips the leap year problem.

I still remember when the church moved the calendar by a couple of weeks - https://en.wikipedia.org/wiki/Gregorian_calendar



That would be the reason why I don't use SQL Server for dates before 1753. ;-) Heh... Y2K was easy after that one. :-P

--Jeff Moden

RBAR is pronounced ree-bar and is a Modenism for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
     Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column.
Although they tell us that they want it real bad, our primary goal is to ensure that we dont actually give it to them that way.
Although change is inevitable, change for the better is not.
Just because you can do something in PowerShell, doesnt mean you should. Wink

Helpful Links:
How to post code problems
How to post performance problems
Forum FAQs
marc.corbeel
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I don't believe it's a correct calculation for all situations. It doesn't look at the first day of a week. In Europe that is Monday, in other parts of the world this is Sunday.
For instance Sunday 3 January 2016 for us in Europe is week 53 (of year 2015). In US this week 1.
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