select SABUNTBL.PORT_CODE as '港コード', PORT.PORT_NAME as '港名', SABUNTBL.IMPAMT as '入国者数', SABUNTBL.EXPAMT as '出国者数', SABUNTBL.SABUN as '差分'
from (select IMP.PORT_CODE, IMPAMT, EXPAMT, IMPAMT-EXPAMT as SABUN 
        from (select PORT_CODE, AMT as IMPAMT from IMMIGRATION where KIND_CODE=110 and group_code=120) imp,
             (select PORT_CODE, AMT as EXPAMT from IMMIGRATION where KIND_CODE=120 and group_code=120) exp
       where IMP.PORT_CODE=EXP.PORT_CODE
     ) SABUNTBL, 
     PORT
where SABUNTBL.PORT_CODE=PORT.PORT_CODE
  and SABUNTBL.SABUN > 0
order by SABUNTBL.SABUN desc,
         SABUNTBL.PORT_CODE desc