SELECT 
    PORT_CODE AS 港コード,
    PORT_NAME AS 港名,
    ENTRY_AMT AS  入国者数,
    DEPARTURE_AMT AS  出国者数,
    (ENTRY_AMT - DEPARTURE_AMT) AS 差分
FROM (
    SELECT
        PORT.PORT_CODE,
        PORT.PORT_NAME,
        SUM(CASE WHEN IMMIGRATION.KIND_CODE='110' THEN IMMIGRATION.AMT ELSE 0 END) AS  ENTRY_AMT,
        SUM(CASE WHEN IMMIGRATION.KIND_CODE='120' THEN IMMIGRATION.AMT ELSE 0 END) AS  DEPARTURE_AMT
    FROM  IMMIGRATION 
    INNER JOIN PORT ON PORT.PORT_CODE = IMMIGRATION.PORT_CODE
    INNER JOIN GRP ON GRP.GROUP_CODE = IMMIGRATION.GROUP_CODE
    WHERE 
        GRP.GROUP_CODE = '120'
    GROUP BY 
        PORT.PORT_CODE
)
WHERE ENTRY_AMT - DEPARTURE_AMT > 0
ORDER BY 
    ENTRY_AMT - DEPARTURE_AMT DESC,
    PORT_CODE DESC