SELECT
    PT.PORT_CODE AS "港コード",
    PT.PORT_NAME AS "港名",
    IM_IN.AMT AS "入国者数",
    IM_OUT.AMT AS "出国者数",
    IM_IN.AMT - IM_OUT.AMT AS "差分"
FROM (SELECT * FROM IMMIGRATION WHERE KIND_CODE = '110') IM_IN
     INNER JOIN (SELECT * FROM IMMIGRATION WHERE KIND_CODE = '120') IM_OUT
         ON IM_IN.PORT_CODE  = IM_OUT.PORT_CODE 
        AND IM_IN.GROUP_CODE = IM_OUT.GROUP_CODE
     INNER JOIN GRP GP
         ON IM_IN.GROUP_CODE = GP.GROUP_CODE
     INNER JOIN PORT PT
         ON IM_IN.PORT_CODE = PT.PORT_CODE
WHERE GP.GROUP_NAME = '外国人'
  AND IM_IN.AMT > IM_OUT.AMT
ORDER BY "差分" DESC, "港コード" DESC