select
po.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 PORT po
left outer join 
(select PORT_CODE, AMT from IMMIGRATION where KIND_CODE = '110' and GROUP_CODE = '120') im1
on po.PORT_CODE = im1.PORT_CODE
left outer join 
(select PORT_CODE, AMT from IMMIGRATION where KIND_CODE = '120' and GROUP_CODE = '120') im2
on po.PORT_CODE = im2.PORT_CODE
where (im1.AMT - im2.AMT) > 0
order by 差分 desc, 港コード desc
;