bit.sql

INSERT INTO x_y
SELECT l.x_id, unnest(array_positions) - 1
FROM (
  SELECT x_y.x_id, bit_or(1 << y.id) AS yids
  FROM x_y
  GROUP BY x_y.x_id
  HAVING count(*) <> (SELECT count(*) FROM y)
) AS l,
reverse(((SELECT bit_or(1 << y.id) FROM y) # l.yids)::bit(64)::text),
string_to_array(reverse, ''),
array_positions(string_to_array, '1');