SELECT
    *
FROM (
SELECT
    PORT_CODE AS 港コード,
    PORT_NAME AS 港名,
    SUM(CASE WHEN KIND_CODE = 110 THEN AMT END)AS 入国者数,
    SUM(CASE WHEN KIND_CODE = 120 THEN AMT END)AS 出国者数,
    SUM(CASE WHEN KIND_CODE = 110 THEN AMT END) - SUM(CASE WHEN KIND_CODE = 120 THEN AMT END)AS 差分
FROM IMMIGRATION
LEFT JOIN PORT
USING(PORT_CODE)
WHERE
    GROUP_CODE = 120
AND
    KIND_CODE IN (110,120)
GROUP BY 1,2
)
WHERE
    差分 > 0
ORDER BY 差分 DESC,港コード