Message-ID: <3D132893.8D0CBF55@Yahoo.com>
Date: Fri, 21 Jun 2002 09:22:27 -0400
From: Jan Wieck <JanWieck@Yahoo.com>
MIME-Version: 1.0
To: Bruno Wolff III <bruno@wolff.to>
Cc: Michael Agbaglo <byteshifter@shifted-bytes.de>,
	josh@agliodbs.com, pgsql-sql@postgresql.org
Subject: Re: how to sort a birthday list ?
References: <3D122508.70104@shifted-bytes.de>
	<200206201703.52435.josh@agliodbs.com>
	<3D12E43E.3090307@shifted-bytes.de>
	<20020621123919.GA11968@wolff.to>
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Bruno Wolff III wrote:
> 
> On Fri, Jun 21, 2002 at 10:30:54 +0200,
>   Michael Agbaglo <byteshifter@shifted-bytes.de> wrote:
> >
> > of course you could sort by DOY but then you'll have a problem w/ the
> > next year:
> >
> > if it's let's say december and you select the list for the next 60 days,
> > persons having birthday in december will appear after persons having
> > birthday in january.
> >
> > I tried to use CASE WHEN... THEN in ORDER BY but it doesn't seem to work
> > (syntax error at '')
> 
> You also need to worry about leap years. If a birthday is February 29
> and there isn't one this year, what do you want to happen?

You can create a little PL/pgSQL function like this:

CREATE FUNCTION next_birthday(date) RETURNS date AS '
DECLARE 
    p_dob       ALIAS FOR $1;
    v_age       integer;
    v_birthday  date;
BEGIN
    -- First we get the age in years
    v_age := EXTRACT (YEAR FROM CURRENT_DATE) - 
             EXTRACT (YEAR FROM p_dob);

    -- We add that to the DOB to get this years birthday
    v_birthday := p_dob + (v_age::text || '' years'')::interval;

    -- If that is in the past, we add another year
    IF v_birthday < CURRENT_DATE THEN
        v_birthday := v_birthday + ''1 year''::interval;
    END IF;

    RETURN v_birthday;
END;'
LANGUAGE plpgsql;

It just calculates the next birthday of a person relative from today.
Then query with

SELECT next_birthday(birthday), name
    FROM person ORDER BY 1;


Jan

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