SELECT
    IMMIGRATION.PORT_CODE as "港コード",
    PORT_NAME as "港名",
    max(case when KIND_CODE = "110" AND GROUP_CODE = "120" THEN AMT  ELSE -1 end) as "入国者数",
    max(case when KIND_CODE = "120" AND GROUP_CODE = "120" THEN AMT  ELSE -1 end) as "出国者数",
    max(case when KIND_CODE = "110" AND GROUP_CODE = "120" THEN AMT  ELSE -1 end) - 
    max(case when KIND_CODE = "120" AND GROUP_CODE = "120" THEN AMT  ELSE -1 end) as "差分"
FROM
    IMMIGRATION
    INNER JOIN PORT ON IMMIGRATION.PORT_CODE = PORT.PORT_CODE
WHERE
    IMMIGRATION.GROUP_CODE = "120" 
GROUP BY 1, 2
HAVING 差分 > 0 
ORDER BY 差分 DESC, 港コード DESC