select
im.PORT_CODE AS 港コード,
po.PORT_NAME AS 港名,
im.AMT AS 入国者数,
im2.AMT AS 出国者数,
(im.AMT - im2.AMT) AS 差分
from
IMMIGRATION as im
join PORT as po on po.PORT_CODE=im.PORT_CODE
join IMMIGRATION as im2 on im2.PORT_CODE=im.PORT_CODE
and im2.GROUP_CODE=im.GROUP_CODE
and im2.KIND_CODE=120
where
im.GROUP_CODE=120
and im.KIND_CODE=110
and 差分 > 0
order by 
差分 desc, im.PORT_CODE desc;