SELECT
    PORT.PORT_CODE AS `港コード`,
    PORT.PORT_NAME AS `港名`,
    IMMIGRANTS.AMT AS `入国者数`,
    DEPARTURES.AMT AS `出国者数`,
    IMMIGRANTS.AMT - DEPARTURES.AMT AS `差分`
FROM
    PORT
INNER JOIN
    IMMIGRATION AS
    IMMIGRANTS ON
    IMMIGRANTS.PORT_CODE = PORT.PORT_CODE AND
    IMMIGRANTS.GROUP_CODE = 120 AND
    IMMIGRANTS.KIND_CODE = 110
INNER JOIN
    IMMIGRATION AS
    DEPARTURES ON
    DEPARTURES.PORT_CODE = PORT.PORT_CODE AND
    DEPARTURES.GROUP_CODE = 120 AND
    DEPARTURES.KIND_CODE = 120
WHERE 
    IMMIGRANTS.AMT - DEPARTURES.AMT > 0
ORDER BY
    `差分` DESC,
    `港コード` DESC