SELECT
  a.PORT_CODE 港コード
  , a.PORT_NAME 港名
  , a.AMT 入国者数
  , b.AMT 出国者数
  , a.AMT - b.AMT 差分
FROM
(
SELECT
  PORT.PORT_CODE
  , PORT.PORT_NAME
  , im.AMT
FROM
  IMMIGRATION im
    inner join PORT on PORT.PORT_CODE = im.PORT_CODE
WHERE
  KIND_CODE = '110'
) a
left join
(
SELECT
  PORT.PORT_CODE
  , PORT.PORT_NAME
  , im.AMT
FROM
  IMMIGRATION im
    inner join PORT on PORT.PORT_CODE = im.PORT_CODE
WHERE
  KIND_CODE = '120'
) b on a.PORT_CODE = b.PORT_CODE
WHERE
  a.AMT - b.AMT > 0
ORDER BY
 a.AMT - b.AMT desc, a.PORT_CODE