SELECT
  i.PORT_CODE 港コード,
  PORT_NAME 港名,
  i.AMT 入国者数,
  ifor.AMT 出国者数,
  (i.AMT - ifor.AMT) AS 差分
FROM
  IMMIGRATION i
INNER JOIN IMMIGRATION ifor
  ON i.PORT_CODE = ifor.PORT_CODE
  AND i.GROUP_CODE = ifor.GROUP_CODE
  AND ifor.KIND_CODE = 120
INNER JOIN PORT p ON i.PORT_CODE = p.PORT_CODE
WHERE
  i.GROUP_CODE = 120
  AND 入国者数 > 出国者数
ORDER BY
  差分 DESC,
  i.PORT_CODE DESC;