SELECT * FROM
(SELECT
    PORT.PORT_CODE AS `港コード`
    ,PORT.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
    INNER JOIN PORT
    ON IMMIGRATION.PORT_CODE = PORT.PORT_CODE AND GROUP_CODE = 120
GROUP BY PORT.PORT_CODE
)
WHERE `差分` > 0
ORDER BY `差分` DESC, `港コード` DESC
;