SELECT
PO.PORT_CODE AS 港コード
,PO.PORT_NAME AS 港名
,sum(IM110.AMT) AS 入国者数
,sum(IM120.AMT) AS 出国者数
,CAST(IM110.AMT AS REAL) - CAST(IM120.AMT AS REAL) AS 差分

FROM
    PORT PO
    LEFT OUTER JOIN IMMIGRATION IM110 on IM110.PORT_CODE = PO.PORT_CODE
    AND IM110.GROUP_CODE = 120
    AND IM110.KIND_CODE = 110
    LEFT OUTER JOIN IMMIGRATION IM120 on IM120.PORT_CODE = PO.PORT_CODE
    AND IM120.GROUP_CODE = 120
    AND IM120.KIND_CODE = 120
    
    
WHERE 
    IM110.AMT >= IM120.AMT

GROUP BY 港コード, 港名

ORDER BY 差分 desc, 港コード desc;