SELECT 
    P.PORT_CODE AS 港コード
    ,P.PORT_NAME AS 港名
    ,SUM(CASE WHEN I.GROUP_CODE = 120 AND KIND_CODE = 110 THEN AMT ELSE 0 END) AS 入国者数
    ,SUM(CASE WHEN I.GROUP_CODE = 110 OR KIND_CODE = 120 THEN AMT ELSE 0 END) AS 出国者数
    ,(SUM(CASE WHEN I.GROUP_CODE = 120 AND KIND_CODE = 110 THEN AMT ELSE 0 END) 
        - SUM(CASE WHEN I.GROUP_CODE = 110 OR KIND_CODE = 120 THEN AMT ELSE 0 END)) AS 差分
FROM 
    IMMIGRATION I JOIN GRP G ON I.GROUP_CODE = G.GROUP_CODE
    JOIN PORT P ON I.PORT_CODE = P.PORT_CODE

GROUP BY P.PORT_CODE
HAVING 差分 > 0
ORDER BY 差分 desc,P.PORT_CODE desc
;