select 
a1.PORT_CODE as 港コード
,a1.PORT_NAME as 港名
,a2.AMT as 入国者数
,a3.AMT as 出国者数
,(a2.AMT - a3.AMT) as 差分
from PORT a1
inner join (
    select i.PORT_CODE,i.AMT from IMMIGRATION i 
        where i.KIND_CODE='110' and i.GROUP_CODE='120'
    ) a2 on a1.PORT_CODE=a2.PORT_CODE
inner join (
    select i.PORT_CODE,i.AMT from IMMIGRATION i 
        where i.KIND_CODE='120' and i.GROUP_CODE='120'
    ) a3 on a1.PORT_CODE=a3.PORT_CODE
where a2.AMT > a3.AMT
order by (a2.AMT - a3.AMT) desc, a1.PORT_CODE desc