Missing Distinct On

-- Gets all rows then filters
SELECT user_id, status
FROM user_status
WHERE (user_id, timestamp) IN (
  SELECT user_id, MAX(timestamp)
  FROM user_status
  GROUP BY user_id
);

-- Uses DISTINCT ON
SELECT DISTINCT ON (user_id) 
  user_id, status
FROM user_status
ORDER BY user_id, timestamp DESC;