SELECT
    PORT_CODE AS '港コード'
    ,PORT_NOME AS '港名'
    ,SUM(CAST(IGT1.AMT)) AS '入国者数'
    ,SUM(CAST(IGT2.AMT)) AS '出国者数'
    ,CAST(IGT1.AMT - IGT2.AMT) AS '差分'
FROM
    IMMIGRATION AS IGT1
    INNER JOIN GRP 
    ON ITG1.GROUP_CODE = GRP.GROUP_CODE
    
    IMMIGRATION AS IGT2
    INNER JOIN AS PORT
    ON IGT2.PORT_CODE = PORT.PORT_CODE
WHERE
    IGT1.GROUP_CODE IN 110
    ,IGT2.GROUP_CODE IN 120
ORDER BY
    '差分' DESC
    PORT.PORT_CODE DESC;