SELECT st.user_id,
        to_json(max(case when id=maxid then properties->'assumed_gender' end)) AS assumed_gender,
        to_json(max(case when id=maxid then properties->'email' end)) AS email,
        to_json(max(case when id=maxid then properties->'first_name' end)) AS first_name,
        to_json(max(case when id=maxid then properties->'last_name' end)) AS last_name,
        to_json(max(case when id=maxid then properties->'country_name' end)) AS country_name,
        to_json(max(case when id=maxid then properties->'city_name' end)) AS city_name,
        to_json(max(case when id=maxid then properties->'mobile_number' end)) AS mobile_number,
        json_agg(to_json(properties->'submission_url')) AS submission_urls
      FROM daily_statistics st JOIN (
          SELECT u.id as user_id, (
          SELECT st2.id FROM daily_statistics st2 WHERE st2.user_id=u.id
          ORDER BY st2.id DESC LIMIT 1) AS maxid FROM users u
        )
        mu ON (st.user_id=mu.user_id)
      GROUP BY st.user_id;

DailyStatistic.select("
  daily_statistics.user_id,
  to_json(max(case when id=maxid then properties->'following' end)),
  to_json(max(case when id=maxid then properties->'assumed_gender' end)),
  to_json(max(case when id=maxid then properties->'email' end)),
  to_json(max(case when id=maxid then properties->'first_name' end)),
  to_json(max(case when id=maxid then properties->'last_name' end)),
  to_json(max(case when id=maxid then properties->'country_name' end)),
  to_json(max(case when id=maxid then properties->'city_name' end)),
  to_json(max(case when id=maxid then properties->'mobile_number' end)),
  json_agg(to_json(properties->'submission_url'))
").join("
  JOIN(
    SELECT u.id as user_id, (
    SELECT st2.id FROM daily_statistics st2 WHERE st2.user_id=u.id
    ORDER BY st2.id DESC LIMIT 1) AS maxid FROM users u
  )
  mu ON (daily_statistics.user_id=mu.user_id)
").group("daily_statistics.user_id")

PG::UndefinedColumn: ERROR:  column "maxid" does not exist
LINE 1: ...aily_statistics.user_id, to_json(max(case when id=maxid then...