WITH A AS (
    SELECT
        IMMIGRATION.PORT_CODE as "港コード",
        PORT_NAME as "港名",
        max(case when KIND_CODE = "110" AND GROUP_CODE = "120" THEN AMT  ELSE -1 end) as "入国者数",
        max(case when KIND_CODE = "120" AND GROUP_CODE = "120" THEN AMT  ELSE -1 end) as "出国者数"
    FROM
        IMMIGRATION
        INNER JOIN PORT ON IMMIGRATION.PORT_CODE = PORT.PORT_CODE
    WHERE
        IMMIGRATION.GROUP_CODE = "120" 
    GROUP BY 1, 2
        ),
    B AS (
    SELECT *
    FROM GRP
    )
SELECT 
    A.港コード,
    A.港名,
    A.入国者数,
    A.出国者数,
    A.入国者数 - A.出国者数 as "差分"
FROM A
WHERE 差分 > 0 
ORDER BY 差分 DESC, 港コード DESC