SELECT IM.PORT_CODE 港コード,PORT_NAME 港名,IM.AMT 入国者数,EX.AMT 出国者数,IM.AMT - EX.AMT 差分
FROM IMMIGRATION AS IM INNER JOIN IMMIGRATION AS EX 
    ON EX.PORT_CODE = IM.PORT_CODE
    AND EX.GROUP_CODE = IM.GROUP_CODE
    AND EX.KIND_CODE = '120'
    INNER JOIN PORT ON IM.PORT_CODE=PORT.PORT_CODE
WHERE IM.GROUP_CODE = '120'
    AND IM.KIND_CODE = '110'
    AND 差分>0
ORDER BY 差分 DESC,港コード DESC