PostgreSQL Functions – How to Return Dynamically Named Column

Since your two types are composed from the same basic types in the same order, they are compatible with each other. So the return type will be the same for functions using them - if I understand correctly, your problem is you want to have the different names of the returned columns depending on the type.

This cannot be done from the database, but you can easily do it from your application. It can be done like (ugly pseudocode)

if type == 1 {
    execute("SELECT 1 AS id_normal_number, '00001' AS normal_number FROM your_function()")
} else {
    execute("SELECT 1 AS id_special_number, 'S0001' AS special_number FROM your_function()")
}

ie. changing only the names, but using the same DB function. Or you can invoke two different functions, this way you can avoid dynamic SQL, which may be desirable for readability/performance, depending on some circumstances.

I don't think you need a cursor here at all. To shorten your code, you could just use a view. To improve performance, a materialized view should get you furthest. Postgres 9.3 has built-in features, but you can easily implemented it in older versions yourself.

Consider this simplified form:

CREATE FUNCTION store_distance(_lat    double precision
                              ,_long   double precision
                              ,_radius double precision
                              ,_tries  integer)
RETURNS TABLE(
   store_id   store.id%type
  ,store_name store.name%type
  ,distance   double precision) AS
$func$
DECLARE
   _ct  int   := 0;
   _pos point := point(_lat, _long);
BEGIN
   LOOP
      EXIT WHEN _ct >= _tries
           OR   EXISTS (
            SELECT 1 FROM store s
            WHERE  point(s.latitude, s.longitude) <@ circle(_pos, _radius));

      _radius := _radius * 2;
      _ct     := _ct + 1;
   END LOOP;

   RETURN QUERY
   SELECT s.id, s.name
         ,get_distance(_lat, _long, s.latitude, s.longitude)
   FROM   store s
   WHERE  point(s.latitude, s.longitude) <@ circle(_pos, _radius);
   ORDER  BY 3;
END
$func$ LANGUAGE plpgsql STRICT;

I made the function STRICT to disallow NULL input, which could result in an endless loop.

Note how I use circles with the "Contained" operator <@ instead of a boxes. One would assume calculations to be slightly more expensive than with boxes, but it hardly matters at all once you support your query with a GiST index like:

CREATE INDEX store_point_gist_idx ON store
USING gist (point(latitude, longitude));

You might consider to store lat / lon as point to begin with and replace the index on an expression with a simpler one on the column. Works either way, just make sure the query matches the index so it gets used. Big difference for big tables.

You may be interested in this closely related answer on SO I posted last year - with a lot more explanation and links.