Re: Week number

On Wed, Mar 14, 2001 at 02:50:35PM +0000, Thomas Lockhart wrote:
> > First day in week is Monday in ISO week.
> > Thomas, we have ISO week-of-year (IW in to_char or 'week' in date_part),
> > but we haven't ISO day-of-week (may be as 'ID' for to_char).
> > TODO for 7.2?
> > ..but in ISO is 0-6; 0=Mon
>
> I've been ignoring this until now, hoping no one would notice ;)
>
> Unix day-of-week starts on Sunday, not Monday, which is what
> date_trunc('dow',...) returns. Presumably this is modeled on the
> traditional notion (at least in the US; I suspect this is true in most
> European countries at least) of Sunday being "the first day of week".
>
> The implementation predates our support of ISO dates so it was not an
> issue then.
>
> date_part() is modeled on Ingres' implementation, but my old Ingres
> manual indicates that 'dow' is not one of the options.
>
> Should we change the definition of "dow", or implement another choice,
> say "idow"?

Yes, I agree with new "idow" for date_part() and 'ID' for to_char() stuff.

My note grow up when I do SQL query that say something like:

"2001-03-12 is begin of week and it's second day of week" .. this sound
very curious :-)

test=# select to_char('2001-03-12'::date, 'IW Dth Day');
to_char
------------------
11 2nd Monday
(1 row)

Karel

--
Karel Zak <zakkr(at)zf(dot)jcu(dot)cz>
http://home.zf.jcu.cz/~zakkr/

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