SELECT
   P.PORT_CODE AS '港コード'
  ,P.PORT_NAME AS '港名'
  ,SUM(I.AMT) AS '入国者数'
  ,SUM(O.AMT) AS '出国者数'
  ,SUM(I.AMT) - SUM(O.AMT) AS '差分'
FROM
  PORT AS P
  LEFT JOIN (SELECT PORT_CODE, AMT FROM IMMIGRATION WHERE KIND_CODE = '110' GROUP BY PORT_CODE) AS I ON P.PORT_CODE = I.PORT_CODE
  LEFT JOIN (SELECT PORT_CODE, AMT FROM IMMIGRATION WHERE KIND_CODE = '120' GROUP BY PORT_CODE) AS O ON P.PORT_CODE = O.PORT_CODE
GROUP BY
  P.PORT_CODE
HAVING
  SUM(I.AMT) > SUM(O.AMT)
ORDER BY
  SUM(I.AMT) - SUM(O.AMT) desc, P.PORT_CODE desc