WITH FOR_IN_AMT AS(
    SELECT
        PORT_CODE
        ,SUM(AMT) AS IN_AMT
    FROM IMMIGRATION
    WHERE GROUP_CODE IN ('120') AND KIND_CODE IN ('110')
    GROUP BY PORT_CODE
)

,FOR_OUT_AMT AS(
    SELECT
        PORT_CODE
        ,SUM(AMT) AS OUT_AMT
    FROM IMMIGRATION
    WHERE GROUP_CODE IN ('120') AND KIND_CODE IN ('120')
    GROUP BY PORT_CODE
)

SELECT
    PORT_CODE AS "港コード"
    ,PORT_NAME AS "港名"
    ,IN_AMT AS "入国者数"
    ,OUT_AMT AS "出国者数"
    ,IN_AMT - OUT_AMT AS "差分"
FROM FOR_IN_AMT NATURAL JOIN FOR_OUT_AMT NATURAL JOIN PORT
WHERE IN_AMT - OUT_AMT > 0
ORDER BY 5 DESC, 1 DESC;