select 
    I.PORT_CODE as 港コード,
    P.PORT_NAME as 港名,
    I.AMT as 入国者数,
    I2.AMT as 出国者数,
    (I.AMT - I2.AMT) as 差分
from 
    IMMIGRATION as I
    inner join IMMIGRATION as I2
        on I.PORT_CODE = I2.PORT_CODE
        and I.GROUP_CODE = I2.GROUP_CODE
        and I2.KIND_CODE = 120
    inner join PORT as P
        on P.PORT_CODE = I.PORT_CODE
where 
    I.GROUP_CODE = 120
    and I.KIND_CODE = 110
    and 差分 > 0
order by 差分 desc, 港コード desc;