SELECT
P.PORT_CODE AS 港コード,
P.PORT_NAME AS 港名,
SUM(SU.AMT) AS 入国者数,
SUM(I.AMT) AS 出国者数,
SUM(SU.AMT - I.AMT) AS  差分
FROM
IMMIGRATION AS I
INNER JOIN 
PORT AS P
ON
I.PORT_CODE = P.PORT_CODE
INNER JOIN 
IMMIGRATION AS SU
ON
I.PORT_CODE = SU.PORT_CODE
AND SU.GROUP_CODE = 120
AND SU.KIND_CODE = 120

WHERE I.GROUP_CODE = 120
AND I.KIND_CODE = 110
AND SU.AMT > I.AMT

GROUP BY P.PORT_CODE
ORDER BY 差分 DESC,
P.PORT_CODE DESC