SELECT
  PRT.PORT_CODE AS '港コード',
  PRT.PORT_NAME AS '港名',
  N_IN AS '入国者数',
  N_OUT AS '出国者数',
  N_IN - N_OUT AS '差分'

FROM PORT AS PRT

JOIN (
  SELECT
      PORT_CODE,
      SUM(AMT) AS 'N_IN'

  FROM IMMIGRATION

  WHERE KIND_CODE = 110
  GROUP BY PORT_CODE
) AS STATS_IN
ON PRT.PORT_CODE = STATS_IN.PORT_CODE

JOIN (
  SELECT
      PORT_CODE,
      SUM(AMT) AS 'N_OUT'

  FROM IMMIGRATION

  WHERE KIND_CODE = 120
  GROUP BY PORT_CODE
) AS STATS_OUT
ON PRT.PORT_CODE = STATS_OUT.PORT_CODE

WHERE N_IN > N_OUT
ORDER BY N_IN - N_OUT DESC, PRT.PORT_CODE ASC
;