SELECT 
    PT.PORT_CODE 港コード
    , PT.PORT_NAME 港名
    , IM110.AMT 入国者数
    , IM120.AMT 出国者数
    , (IM110.AMT - IM120.AMT) 差分 
FROM PORT PT
    INNER JOIN IMMIGRATION IM110
        ON PT.PORT_CODE = IM110.PORT_CODE
        AND IM110.KIND_CODE = "110"
    INNER JOIN IMMIGRATION IM120
        ON PT.PORT_CODE = IM120.PORT_CODE
        AND IM120.KIND_CODE = "120"
WHERE IM110.GROUP_CODE = "120"
    AND IM120.GROUP_CODE = "120"
    AND 差分 > 0  
GROUP BY 港コード, 港名, 入国者数, 出国者数
ORDER BY 差分 DESC, 港コード DESC;