select
    I.PORT_CODE as 港コード,
    P.PORT_NAME as 港名,
    入国者数,
    出国者数,
    入国者数 - 出国者数 as 差分
From 
    PORT P
LEFT JOIN (Select PORT_CODE,AMT as 入国者数 From IMMIGRATION I Where KIND_CODE = '110' AND GROUP_CODE='120') as I ON I.PORT_CODE = P.PORT_CODE
LEFT JOIN (Select PORT_CODE,AMT as 出国者数 From IMMIGRATION I Where KIND_CODE = '120' AND GROUP_CODE='120') as O ON O.PORT_CODE = P.PORT_CODE
Where
    入国者数 > 出国者数
order by
    差分 desc
    , 港コード desc