SELECT
   IC.PORT_CODE AS "港コード"
  ,P.PORT_NAME AS "港名"
  ,IC.AMT  AS "入国者数"
  ,OC.AMT  AS "出国者数"
  ,IC.AMT  - OC.AMT  AS "差分"
FROM
  IMMIGRATION IC
  INNER JOIN
  IMMIGRATION OC
  ON 
    IC.PORT_CODE = OC.PORT_CODE
  INNER JOIN
  PORT P
  ON IC.PORT_CODE = P.PORT_CODE
  AND IC.AMT > OC.AMT
WHERE
      IC.KIND_CODE='110'
  AND OC.KIND_CODE='120'
  AND IC.GROUP_CODE='120'
  AND OC.GROUP_CODE='120'
ORDER BY
  差分 DESC,IC.PORT_CODE DESC
  ;