gistfile1.sql

CREATE TABLE a (id serial, x int);

INSERT INTO a (x) VALUES (5);
INSERT INTO a (x) VALUES (7);
INSERT INTO a (x) VALUES (11);
INSERT INTO a (x) VALUES (13);

--- first data
SELECT * FROM a;

--- return the old data rows from the result
WITH old_data AS (
  SELECT id, x
  FROM a
)
UPDATE a
SET x = 1
FROM old_data
WHERE old_data.id = a.id
RETURNING old_data.x;

-- show that data has been updated
SELECT * FROM a;