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