SELECT IMM.PORT_CODE AS 港コード,
       POR.PORT_NAME AS 港名,
       IMM.AMT AS 入国者数,
       IMM2.AMT AS 出国者数,
       (IMM.AMT-IMM2.AMT) AS 差分
       
FROM IMMIGRATION AS IMM
      INNER JOIN IMMIGRATION AS IMM2
        ON IMM2.PORT_CODE =IMM.PORT_CODE
        AND IMM2.GROUP_CODE= IMM.GROUP_CODE
        AND IMM2.KIND_CODE='120'
      INNER JOIN PORT AS POR
        ON POR.PORT_CODE=IMM.PORT_CODE

WHERE IMM.GROUP_CODE ='120'
      AND IMM.KIND_CODE='110'
      AND 差分>0

ORDER BY 差分 DESC,港コード DESC;