SELECT
 IM1.PORT_CODE AS 港コード,
 PORT_NAME AS 港名,
 IM1.AMT AS 入国者数,
 IM2.AMT AS 出国者数,
 IM1.AMT - IM2.AMT AS 差分

FROM
 IMMIGRATION AS IM1
  INNER JOIN IMMIGRATION AS IM2 
   ON IM2.PORT_CODE = IM1.PORT_CODE
   AND IM2.GROUP_CODE = IM1.GROUP_CODE
   AND IM2.KIND_CODE = '120'
 
 
  INNER JOIN PORT AS PORT
   ON IM1.PORT_CODE = PORT.PORT_CODE
  INNER JOIN GRP AS GRP
   ON IM1.GROUP_CODE = GRP.GROUP_CODE

WHERE
 IM1.KIND_CODE = '110'
 AND GRP.GROUP_NAME = '外国人'
 AND 差分 > 0  
ORDER BY
 差分 DESC,
 港コード DESC;