SELECT B.PORT_CODE AS 港コード,
       B.PORT_NAME AS 港名,
       SUM(CASE WHEN A.KIND_CODE = '110' THEN A.AMT ELSE 0 END) AS 入国者数,
       SUM(CASE WHEN A.KIND_CODE = '120' THEN A.AMT ELSE 0 END) AS 出国者数,
       SUM(CASE WHEN A.KIND_CODE = '110' THEN A.AMT WHEN A.KIND_CODE = '120' THEN -A.AMT ELSE 0 END) AS 差分
FROM IMMIGRATION AS A
     LEFT OUTER JOIN PORT AS B ON A.PORT_CODE = B.PORT_CODE
     LEFT OUTER JOIN GRP  AS C ON A.GROUP_CODE = C.GROUP_CODE
WHERE GROUP_NAME = '外国人' AND KIND_CODE IN ('110', '120')
GROUP BY 港コード, 港名
HAVING 差分 > 0
ORDER BY 差分 DESC, 港コード DESC;