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