SELECT
    a.PORT_CODE   港コード
    , b.PORT_NAME 港名
    , SUM(CASE WHEN KIND_CODE = 110 THEN a.AMT ELSE 0 END) 入国者数
    , SUM(CASE WHEN KIND_CODE = 120 THEN a.AMT ELSE 0 END) 出国者数
    , SUM((CASE WHEN KIND_CODE = 110 THEN a.AMT ELSE 0 END) - (CASE WHEN KIND_CODE = 120 THEN a.AMT ELSE 0 END)) 差分

FROM
    IMMIGRATION a
        LEFT JOIN PORT b
            on a.PORT_CODE = b.PORT_CODE

GROUP BY
    a.PORT_CODE
    , b.PORT_NAME

HAVING
    入国者数 > 出国者数

ORDER BY
    差分 DESC
    , a.PORT_CODE DESC
;