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