CREATE OR REPLACE FUNCTION customersInCity (TEXT, REFCURSOR) returns REFCURSOR AS 
$$
DECLARE
   cityName TEXT := $1;
   resultSet REFCURSOR := $2;
BEGIN
   OPEN resultSet for
      select *
      from people
      where homeCity = cityName;
   return resultSet;
END;
$$
LANGUAGE PLPGSQL;

select customersInCity('Toronto', 'results');
fetch all from results;