SELECT
PORT_CODE as '港コード',
PORT_NAME as '港名',
IN_AMT as '入国者数',
OUT_AMT as '出国者数',
CALC as '差分'
FROM
(
 SELECT 
 INA.PORT_CODE ,
 INA.PORT_NAME ,
 INA.IN_AMT,
 OUTA.OUT_AMT,
 INA.IN_AMT - OUTA.OUT_AMT as 'CALC'
 FROM
 (
  SELECT 
   P.PORT_CODE,
   P.PORT_NAME,
   I.AMT AS 'OUT_AMT'
  FROM 
   IMMIGRATION I
   INNER JOIN PORT P
   ON I.PORT_CODE = P.PORT_CODE
   INNER JOIN GRP G
   ON I.GROUP_CODE = G.GROUP_CODE
  WHERE
   G.GROUP_CODE = '120'
   AND I.KIND_CODE = '120'
 ) OUTA
 INNER JOIN (
  SELECT
   P.PORT_CODE,
   P.PORT_NAME,
   I.AMT AS 'in_AMT'
  FROM
   IMMIGRATION I
   INNER JOIN PORT P
   ON I.PORT_CODE = P.PORT_CODE
   INNER JOIN GRP G
   ON I.GROUP_CODE = G.GROUP_CODE
   WHERE
   G.GROUP_CODE = '120'
   AND I.KIND_CODE = '110'
 ) INA
 ON OUTA.PORT_CODE = INA.PORT_CODE
)
WHERE
CALC > 0
ORDER BY
CALC desc,PORT_CODE desc