SELECT
  PORT.PORT_CODE AS "港コード"
, PORT.PORT_NAME AS "港名"
, COALESCE(IM1.AMT, 0) AS "入国者数"
, COALESCE(IM2.AMT, 0) AS "出国者数"
, COALESCE(IM1.AMT, 0) -  COALESCE(IM2.AMT, 0) AS "差分"
FROM PORT
LEFT JOIN IMMIGRATION AS IM1 ON
(
    IM1.PORT_CODE = PORT.PORT_CODE
  AND
    IM1.GROUP_CODE = 120
  AND
    IM1.KIND_CODE = 110
)
LEFT JOIN IMMIGRATION AS IM2 ON
(
    IM2.PORT_CODE = PORT.PORT_CODE
  AND
    IM2.GROUP_CODE = 120
  AND
    IM2.KIND_CODE = 120
)
WHERE
  IM1.AMT IS NOT NULL
AND
  IM2.AMT IS NOT NULL
AND
  COALESCE(IM1.AMT, 0) -  COALESCE(IM2.AMT, 0) > 0
ORDER BY
  "差分" DESC
, "港コード" DESC
;