SELECT main.PORT_CODE AS 港コード
      ,main.PORT_NAME AS 港名
      ,sub.NumIn      AS 入国者数
      ,sub.NumOut     AS 出国者数
      ,sub.NumIn - sub.NumOut AS 差分
FROM PORT main
INNER JOIN (
SELECT a.PORT_CODE
      ,SUM(CASE WHEN a.KIND_CODE = '110' THEN a.AMT ELSE 0 END) AS NumIn
      ,SUM(CASE WHEN a.KIND_CODE = '120' THEN a.AMT ELSE 0 END) AS NumOut     
FROM IMMIGRATION a
INNER JOIN GRP b
ON a.GROUP_CODE = b.GROUP_CODE
AND b.GROUP_NAME = '外国人'
GROUP BY a.PORT_CODE
HAVING NumIn > NumOut
)sub
ON main.PORT_CODE = sub.PORT_CODE
WHERE sub.NumIn > sub.NumOut
ORDER BY sub.NumIn - sub.NumOut DESC