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 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;