SELECT
  IMMIGRATION.PORT_CODE AS 港コード,
  PORT.PORT_NAME AS 港名,
  SUM(CASE WHEN IMMIGRATION.KIND_CODE = 110 THEN IMMIGRATION.AMT ELSE 0 END) AS 入国者数,
  SUM(CASE WHEN IMMIGRATION.KIND_CODE = 120 THEN IMMIGRATION.AMT ELSE 0 END) AS 出国者数,
  SUM(CASE WHEN IMMIGRATION.KIND_CODE = 110 THEN IMMIGRATION.AMT ELSE 0 END) - SUM(CASE WHEN KIND_CODE = 120 THEN AMT ELSE 0 END) AS 差分
FROM
  IMMIGRATION
INNER JOIN
  PORT
ON
  IMMIGRATION.PORT_CODE = PORT.PORT_CODE
WHERE
  GROUP_CODE = "120"
GROUP BY
  港コード,
  港名
HAVING
  差分 > 0
ORDER BY
  差分 DESC,
  港コード DESC