SELECT
     MAIN.PORT_CODE AS 港コード
    ,PORT.PORT_NAME AS 港名
    ,外国人入国者のAMT        AS  入国者数
    ,外国人出国者のAMT        AS 出国者数
    ,外国人入国者のAMT-外国人出国者のAMT AS 差分
FROM (
SELECT 
     IMM.PORT_CODE 
    ,SUM(CASE WHEN  IMM.KIND_CODE = '110' THEN IMM.AMT ELSE 0 END ) 外国人入国者のAMT 
    ,SUM(CASE WHEN  IMM.KIND_CODE = '120' THEN IMM.AMT ELSE 0 END ) 外国人出国者のAMT 
FROM IMMIGRATION IMM
WHERE GROUP_CODE = 120
GROUP BY IMM.PORT_CODE) MAIN
LEFT OUTER JOIN PORT
ON MAIN.PORT_CODE = PORT.PORT_CODE
WHERE MAIN.外国人入国者のAMT >=  MAIN.外国人出国者のAMT
ORDER BY 外国人入国者のAMT-外国人出国者のAMT  DESC,MAIN.PORT_CODE DESC