SELECT DISTINCT
  *
FROM
  (
SELECT
  por.PORT_CODE AS "港コード",
  por.PORT_NAME AS "港名",
  SUM(CASE WHEN imm.KIND_CODE = '110' THEN imm.AMT ELSE NULL END) OVER(PARTITION BY por.PORT_CODE) AS "入国者数",
  SUM(CASE WHEN imm.KIND_CODE = '120' THEN imm.AMT ELSE NULL END) OVER(PARTITION BY por.PORT_CODE) AS "出国者数",
  SUM(CASE WHEN imm.KIND_CODE = '110' THEN imm.AMT ELSE NULL END) OVER(PARTITION BY por.PORT_CODE) - SUM(CASE WHEN imm.KIND_CODE = '120' THEN imm.AMT ELSE NULL END) OVER(PARTITION BY por.PORT_CODE) AS "差分"
FROM
  IMMIGRATION AS imm
LEFT OUTER JOIN
  PORT AS por
ON
  imm.PORT_CODE = por.PORT_CODE
WHERE
  imm.GROUP_CODE = '120'
  )
WHERE
  "差分" >= 0
ORDER BY
  "差分" desc,
  "港コード" desc