WITH pre_in AS (
    SELECT
        PORT_CODE,
        AMT AS "入国者数"
    FROM
        IMMIGRATION
    WHERE
        GROUP_CODE = 120 AND KIND_CODE = 110
), pre_out AS (
    SELECT
        PORT_CODE,
        AMT AS "出国者数"
    FROM
        IMMIGRATION
    WHERE
        GROUP_CODE = 120 AND KIND_CODE = 120
)

SELECT
    PORT_CODE AS 港コード,
    PORT_NAME AS 港名,
    入国者数,
    出国者数,
    (入国者数 - 出国者数) AS 差分
FROM
    pre_in
LEFT JOIN
    pre_out USING (PORT_CODE)
LEFT JOIN
    PORT USING (PORT_CODE)
WHERE
    差分 > 0
ORDER BY
    差分 DESC