ROW_NUMBER（）使用DATEDIFF输出作为排序失败

Question

谁能告诉我为什么这会引发错误？

WITH date_diffs AS 
(
   SELECT
       ctd_item_id,
       ctd_assigned_to,
       DATEDIFF(d, ctd_assigned_date, ctd_review_completed_date) AS DATE_DIFF,
       ROW_NUMBER() OVER (PARTITION BY ctd_item_id ORDER BY date_diff DESC) AS RN 
   FROM
       irt_item_tracking_detail_tbl
)
SELECT
    * 
FROM
    date_diffs 
WHERE
    date_diffs.rn = 1

错误是

  

无效的列名“ date_diff”

不能在SELECT的{​​{1}}语句中创建它吗？