SELECT
  IMMIGRATION.PORT_CODE AS 港コード,
  PORT.PORT_NAME AS 港名,
  SUM(CASE WHEN IMMIGRATION.GROUP_CODE = 110 THEN AMT ELSE 0 END) AS 入国者数,
  SUM(CASE WHEN IMMIGRATION.GROUP_CODE = 120 THEN AMT ELSE 0 END) AS 出国者数,
  SUM(CASE WHEN IMMIGRATION.GROUP_CODE = 110 THEN AMT ELSE 0 END) - SUM(CASE WHEN IMMIGRATION.GROUP_CODE = 110 THEN AMT ELSE 0 END) AS 差分
FROM
  IMMIGRATION
INNER JOIN
  PORT
  ON IMMIGRATION.PORT_CODE = PORT.PORT_CODE
GROUP BY
  IMMIGRATION.PORT_CODE,
  PORT.PORT_NAME
HAVING BY
 差分 > 0
ORDER BY
  5,
  1