Re: Fastest way / best practice to calculate "next birthdays"

Hannes Dorbath írta:
> Joshua D. Drake wrote:
>> postgres=# SELECT current_date|| ' a ' || to_char(current_date, 'Day'),
>> current_date + '1 Year'::interval || ' a '  || to_char(current_date +
>> '1 Year'::interval, 'Day') as next_birthday;
>>         ?column?        |          next_birthday
>> ------------------------+---------------------------------
>>  2008-05-04 a Sunday    | 2009-05-04 00:00:00 a Monday
>>
>> ?
>
> Sorry, I think I phrased the question badly. What I'm after basically is:
>
> http://www.depesz.com/index.php/2007/10/26/who-has-birthday-tomorrow/

If you define the same functional index as in the above link:

CREATE OR REPLACE FUNCTION indexable_month_day(date) RETURNS TEXT as $BODY$
SELECT to_char($1, 'MM-DD');
$BODY$ language 'sql' IMMUTABLE STRICT;

create table user_birthdate (
  id serial not null primary key,
  birthdate date
);
create index user_birthdate_day_idx on user_birthdate (
indexable_month_day(birthdate) );

Then you can use this query:

select count(*) from user_birthdate where indexable_month_day(birthdate)
 > '02-28' and indexable_month_day(birthdate) <= '03-01';

In a generic and parametrized way:

select * from user_birthdate
where
  indexable_month_day(birthdate) > indexable_month_day(now()::date) and
  indexable_month_day(birthdate) <= indexable_month_day((now() + '1
days'::interval)::date);

This will still use the index and it will work for the poor ones
who have birthday every 4 years, too. Assume, it's 02-08 today, 03-01
the next day.
The now() < X <= now() + 1 day range will find 02-29.

--
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Zoltán Böszörményi
Cybertec Schönig & Schönig GmbH
http://www.postgresql.at/