select

PORT.PORT_CODE as 港コード,
PORT.PORT_NAME as 港名
,
IMMIGRATION110.amt as "入国者数"
,
IMMIGRATION120.amt as "出国者数"

,IMMIGRATION110.amt - IMMIGRATION120.amt as 差分

from (
select *
from 
IMMIGRATION
where KIND_CODE = "120" and GROUP_CODE = "120"
) IMMIGRATION120
join  (
select *
from 
IMMIGRATION
where KIND_CODE = "110" and GROUP_CODE = "120"
) IMMIGRATION110
on IMMIGRATION120.PORT_CODE = IMMIGRATION110.PORT_CODE
and  IMMIGRATION120.GROUP_CODE = IMMIGRATION110.GROUP_CODE
left outer JOIN  PORT
on IMMIGRATION120.PORT_CODE = PORT.PORT_CODE

where 差分 > 0

-- group by PORT.PORT_CODE
order by 差分 desc, 港コード desc