WITH IN_COUNTRY AS (
  SELECT * FROM IMMIGRATION
  WHERE 
    GROUP_CODE = 120
    AND KIND_CODE = 110
    
), OUT_COUNTRY AS (
  SELECT * FROM IMMIGRATION
  WHERE 
    GROUP_CODE = 120
    AND KIND_CODE = 120
)

SELECT 
  p.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 
  PORT AS p
INNER JOIN 
  IN_COUNTRY AS i
ON p.PORT_CODE = i.PORT_CODE

INNER JOIN 
  OUT_COUNTRY AS o
ON p.PORT_CODE = o.PORT_CODE

WHERE 
  (i.AMT - o.AMT) > 0

ORDER BY 
  差分 DESC,
  港コード DESC