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