SELECT main.PORT_CODE AS 港コード
      ,sub.PORT_NAME  AS 港名
      ,main.AMT_IN    AS 入国者数
      ,main.AMT_OUT   AS 出国者数
      ,main.AMT_DIF   AS 差分
FROM(
SELECT a.PORT_CODE
      ,MAX(a.AMT) FILTER(WHERE a.KIND_CODE = '110') AS AMT_IN
      ,MAX(a.AMT) FILTER(WHERE a.KIND_CODE = '120') AS AMT_OUT    
      ,MAX(a.AMT) FILTER(WHERE a.KIND_CODE = '110') - MAX(a.AMT) FILTER(WHERE a.KIND_CODE = '120') AS AMT_DIF
FROM IMMIGRATION a
WHERE a.GROUP_CODE = '120'
GROUP BY a.PORT_CODE
)main
INNER JOIN PORT sub
ON main.PORT_CODE = sub.PORT_CODE
WHERE main.AMT_DIF > 0
ORDER BY main.AMT_DIF DESC
        ,main.PORT_CODE DESC