select
 a.PORT_CODE as 港コード
,a.PORT_NAME as 港名
,b.AMT as 入国者数
,c.AMT as 出国者数
,b.AMT - c.AMT as 差分
from PORT a
left join IMMIGRATION b
 on a.PORT_CODE = b.PORT_CODE
and b.KIND_CODE = '110'
and b.GROUP_CODE = '120'
left join IMMIGRATION c
 on a.PORT_CODE = c.PORT_CODE
and c.KIND_CODE = '120'
and c.GROUP_CODE = '120'
where 1=1
and b.AMT > c.AMT
order by 差分 desc, a.PORT_CODE desc