Thread: How can I get the first and last date of a week, based on the week number and the year
How can I get the first and last date of a week, based on the week number and the year
From
Bruno Baguette
Date:
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 ? Many thanks in advance ! Regards, -- Bruno Baguette - bruno.baguette@gmail.com
Re: How can I get the first and last date of a week, based on the week number and the year
From
Adrian Klaver
Date:
On Tuesday 26 February 2008 5:32 pm, 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 ?
>
> Many thanks in advance !
>
> Regards,
This will get you to the Monday of the week .
select to_date('9 08','IW YY');
to_date
------------
2008-02-25
(1 row)
Where 9 is the ISO week number and 08 is the year. See below for more details:
http://www.postgresql.org/docs/8.2/interactive/functions-formatting.html
--
Adrian Klaver
aklaver@comcast.net
Re: How can I get the first and last date of a week, based on the week number and the year
From
brian
Date:
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 ? > Use pl/Perl and the Date::Calc module.
Re: How can I get the first and last date of a week, based on the week number and the year
From
Tom Lane
Date:
Adrian Klaver <aklaver@comcast.net> writes:
> On Tuesday 26 February 2008 5:32 pm, Bruno Baguette wrote:
>> 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.
> This will get you to the Monday of the week .
> select to_date('9 08','IW YY');
> to_date
> ------------
> 2008-02-25
> (1 row)
date_trunc('week', ...) would probably be a more convenient way of doing
that.
regards, tom lane
Re: How can I get the first and last date of a week, based on the week number and the year
From
Adrian Klaver
Date:
On Tuesday 26 February 2008 8:39 pm, Tom Lane wrote:
> Adrian Klaver <aklaver@comcast.net> writes:
> > On Tuesday 26 February 2008 5:32 pm, Bruno Baguette wrote:
> >> 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.
> >
> > This will get you to the Monday of the week .
> >
> > select to_date('9 08','IW YY');
> > to_date
> > ------------
> > 2008-02-25
> > (1 row)
>
> date_trunc('week', ...) would probably be a more convenient way of doing
> that.
>
> regards, tom lane
I am not sure I follow. The OP has a ISO week number and a year and wants
dates. I thought date_trunc('field',source) requires a timestamp or interval
as its source.
--
Adrian Klaver
aklaver@comcast.net
Re: How can I get the first and last date of a week, based on the week number and the year
From
Tom Lane
Date:
Adrian Klaver <aklaver@comcast.net> writes:
> On Tuesday 26 February 2008 8:39 pm, Tom Lane wrote:
>> date_trunc('week', ...) would probably be a more convenient way of doing
>> that.
> I am not sure I follow. The OP has a ISO week number and a year and wants
> dates. I thought date_trunc('field',source) requires a timestamp or interval
> as its source.
Oh, you are right ... I misread the question :-(
regards, tom lane
Re: How can I get the first and last date of a week, based on the week number and the year
From
Richard Huxton
Date:
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.
Broken down step-by-step. End of week left as an exercise
SELECT
doy,
EXTRACT(dow FROM doy) AS offset,
(doy - EXTRACT(dow FROM doy) * '1 day'::interval)::date AS start_of_week
FROM
(SELECT ('2008-01-04'::date + 8 * '1 week'::interval)::date AS doy)
AS foo;
doy | offset | start_of_week
------------+--------+---------------
2008-02-29 | 5 | 2008-02-24
(1 row)
--
Richard Huxton
Archonet Ltd
Re: How can I get the first and last date of a week, based on the week number and the year
From
Alban Hertroys
Date:
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
--
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