SELECT
  x.port_code AS "港コード",
  p.port_name AS "港名",
  x.amt AS "入国者数",
  y.amt AS "出国者数",
  (x.amt - y.amt) AS "差分"
FROM
  (
    SELECT
      *
    FROM
      immigration
    WHERE
      kind_code = 110
      AND group_code = 120
  ) x
  JOIN (
    SELECT
      *
    FROM
      immigration
    WHERE
      kind_code = 120
      AND group_code = 120
  ) y ON x.port_code = y.port_code
  AND x.group_code = y.group_code
  JOIN port p ON x.port_code = p.port_code
WHERE
  "差分" > 0
ORDER BY
  "差分" DESC,
  x.port_code DESC;