CREATE FUNCTION mise_a_jour_t2() RETURNS trigger AS '
  BEGIN
    IF TG_OP = 'INSERT' OR TG_OP = 'UPDATE' THEN
      UPDATE table2 SET champ2 = champ2 + 1 WHERE... ;
      RETURN NEW;
    ELSE IF TG_OP = 'DELETE'
      UPDATE table2 SET champ2 = champ2 - 1 WHERE ... ;
      RETURN OLD ;
    END IF;
  END;

' LANGUAGE plpgsql;

CREATE TRIGGER mise_a_jour 
  AFTER INSERT OR UPDATE OR DELETE 
  ON table1
  FOR EACH ROW EXECUTE PROCEDURE mise_a_jour_t2();