Re: How can I get the first and last date of a week, based on the week number and the year

[Alban Hertroys <dalroi(at)solfertje(dot)student(dot)utwente(dot)nl>]

On Feb 27, 2008, at 2:32 AM, Bruno Baguette wrote:

> Hello !
>
> I have a week number (ISO 8601) and a year, based on theses values,  
> I would like to get the first and the last dates of that week.
>
> How I can do that ?
>
> The only solution is doing a big generate_series to build a subset  
> that contains the week of all the dates between the 01/01 || year  
> and the 31/12 || year. But I find that solution quite dirty and  
> ressources consumming.
>
> Is there a cleanest way to do that ?

You can use to_date for most of that, like:
development=> select to_date('01 02 2008', 'ID IW YYYY') AS start,
	to_date('07 02 2008', 'ID IW YYYY') AS end;
   start    |    end
------------+------------
 2008-01-07 | 2008-01-07
(1 row)

I'm a bit surprised that specifying the weekdays doesn't make any  
difference here, maybe it's my version?:

development=> select version();
                                            version
------------------------------------------------------------------------ 
------------------------
 PostgreSQL 8.2.4 on i386-portbld-freebsd6.2, compiled by GCC cc  
(GCC) 3.4.6 [FreeBSD] 20060305
(1 row)


Anyway, you can solve that by adding an interval '6 days' to the end  
result.

Alban Hertroys

--
If you can't see the forest for the trees,
cut the trees and you'll see there is no forest.


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