create table capaxy (gid serial primary key, x double precision, y double precision);
select addgeometrycolumn ('','capaxy','geom',-1,'POINT',2);

BEGIN TRANSACTION;

CREATE OR REPLACE FUNCTION tggFunction_updateEventos() RETURNS trigger AS
$$
  BEGIN
    IF ((NEW.x != OLD.x) OR (NEW.y != OLD.y)) THEN
      NEW.geom = ST_MAKEPOINT (NEW.x, NEW.y);
    ELSE ...