returning problem

schema.sql

CREATE TABLE pis1
(
  x serial NOT NULL,
  y integer,
  CONSTRAINT pk_lineas PRIMARY KEY (x)
);


CREATE TABLE pis2
(
  id serial,
  x integer,
  y integer,
  CONSTRAINT pk_lineas PRIMARY KEY (id),
  CONSTRAINT lineas_id_pred_pasado_fkey FOREIGN KEY (x)
      REFERENCES pis1 (x) MATCH SIMPLE
      ON UPDATE CASCADE ON DELETE CASCADE
);


INSERT INTO pis2 (x) SELECT pis1.x FROM pis1 JOIN  generate_series(1,3) as kk ON pis1.y = kk RETURNING id,kk;