select
    IMMIGRATION.PORT_CODE as 港コード,
    PORT_NAME as 港名,
    in_i.入国者数,
    ex_i.出国者数,
    (in_i.入国者数 - ex_i.出国者数) as 差分
    -- 外国人入国者のAMT as 入国者数,
    -- 外国人出国者のAMT as 出国者数,
    -- 外国人入国者のAMT - 外国人出国者のAMTの計算結果 as 差分
from IMMIGRATION
inner join PORT on (
    PORT.PORT_CODE = IMMIGRATION.PORT_CODE
    )
inner join (select PORT_CODE, sum(IMMIGRATION.AMT) as 入国者数 from IMMIGRATION where KIND_CODE = '110' group by PORT_CODE) as in_i
    on (in_i.PORT_CODE = IMMIGRATION.PORT_CODE)
inner join (select PORT_CODE, sum(IMMIGRATION.AMT) as 出国者数 from IMMIGRATION where KIND_CODE = '120' group by PORT_CODE) as ex_i
    on (ex_i.PORT_CODE = IMMIGRATION.PORT_CODE)
group by IMMIGRATION.PORT_CODE
having 差分 > 0
order by 差分 desc