SELECT
  t.PORT_CODE AS "港コード",
  PORT.PORT_NAME AS "港名",
  nyukoku_num AS "入国者数",
  shukkoku_num AS "出国者数",
  nyukoku_num - shukkoku_num AS "差分"

FROM
  (
    SELECT
      PORT_CODE,
      SUM(CASE WHEN GROUP_CODE = '110' THEN AMT ELSE 0 END) AS nyukoku_num,
      SUM(CASE WHEN GROUP_CODE = '120' THEN AMT ELSE 0 END) AS shukkoku_num
    FROM
      IMMIGRATION
    GROUP BY
      PORT_CODE
  ) t

INNER JOIN
  PORT
ON
  t.PORT_CODE = PORT.PORT_CODE 
  
WHERE
  nyukoku_num - shukkoku_num >0
ORDER BY
  nyukoku_num - shukkoku_num DESC,
  t.PORT_CODE DESC