SELECT
IM1.PORT_CODE AS 港コード,
PO.PORT_NAME AS 港名,
IM1.AMT AS 入国者数,
IM2.AMT AS 出国者数,
(IM1.AMT - IM2.AMT) AS 差分
FROM
IMMIGRATION AS IM1
INNER JOIN IMMIGRATION AS IM2 
ON IM1.PORT_CODE = IM2.PORT_CODE 
AND IM1.GROUP_CODE = IM2.GROUP_CODE
AND IM2.KIND_CODE = '120' 
INNER JOIN PORT AS PO
ON PO.PORT_CODE = IM1.PORT_CODE

WHERE
IM1.GROUP_CODE = "110"
IM2.GROUP_CODE = "120"
差分 > 0

ORDER BY 
差分 DESC,
IM1.PORT_CODE DESC;