SELECT
*
FROM
(SELECT 
PO.PORT_CODE AS 港コード,
PORT_NAME AS 港名,
SUM(case WHEN KIND_CODE=110 THEN AMT ELSE 0 END) AS 入国者数,
SUM(case WHEN KIND_CODE=120 THEN AMT ELSE 0 END) AS 出国者数,
SUM(case WHEN KIND_CODE=110 THEN AMT ELSE 0 END) - SUM(case WHEN KIND_CODE=120 THEN AMT ELSE 0 END) AS 差分
FROM IMMIGRATION AS IM
JOIN 
PORT AS PO ON IM.PORT_CODE = PO.PORT_CODE
WHERE GROUP_CODE = 120
AND KIND_CODE IN (110, 120)
GROUP BY 港コード
)
WHERE 差分 > 0
ORDER BY 差分 DESC, 港コード DESC;