How do you do date math that ignores the year?

Question

I am trying to select dates that have an anniversary in the next 14 days. How can I select based on dates excluding the year? I have tried something like the following.

Answer 1

For convenience, I created two functions that yield the (expected or past) birsthday in the current year, and the upcoming birthday.

CREATE OR REPLACE FUNCTION this_years_birthday( _dut DATE) RETURNS DATE AS
$func$

DECLARE
        ret DATE;
BEGIN
        ret =
        date_trunc( 'year' , current_timestamp)
        + (date_trunc( 'day' , _dut)
          - date_trunc( 'year' , _dut)
          )
        ;
        RETURN ret;
END;
$func$ LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION next_birthday( _dut DATE) RETURNS DATE AS
$func$

DECLARE
        ret DATE;
BEGIN
        ret =
        date_trunc( 'year' , current_timestamp)
        + (date_trunc( 'day' , _dut)
          - date_trunc( 'year' , _dut)
          )
        ;
        IF (ret < date_trunc( 'day' , current_timestamp))
           THEN ret = ret + '1year'::interval; END IF;
        RETURN ret;
END;
$func$ LANGUAGE plpgsql;

      --
      -- call the function
      --
SELECT date_trunc( 'day' , t.topic_date) AS the_date
        , this_years_birthday( t.topic_date::date ) AS the_day
        , next_birthday( t.topic_date::date ) AS next_day
FROM topic t
WHERE this_years_birthday( t.topic_date::date )
        BETWEEN  current_date
        AND  current_date + '2weeks':: interval
        ;

NOTE: the casts are needed because I only had timestamps available.