SELECT
    IM.PORT_CODE AS 港コード
    ,PO.PORT_NAME AS 港名
    ,SUM(CASE WHEN KIND_CODE=110 THEN AMT END) AS 入国者数
    ,SUM(CASE WHEN KIND_CODE=120 THEN AMT END) AS 出国者数
    ,SUM(CASE WHEN KIND_CODE=110 THEN AMT END)  - SUM(CASE WHEN KIND_CODE=120 THEN AMT END) AS 差分
FROM IMMIGRATION IM
LEFT JOIN GRP 
ON IM.GROUP_CODE = GRP.GROUP_CODE
LEFT JOIN PORT PO
ON IM.PORT_CODE = PO.PORT_CODE
WHERE 
    GRP.GROUP_CODE = 120 
GROUP BY IM.PORT_CODE
HAVING 入国者数>出国者数
ORDER BY 差分 DESC, 港コード DESC