可以參考以下的方法
UPDATE UpdateTarget
SET seq = rownum
FROM (
SELECT seq, row_number () OVER (ORDER BY seq) rownum
FROM Table
WHERE no = @no
) UpdateTarget
Ref: https://codeday.me/bug/20180808/213927.html
UPDATE UpdateTarget
SET seq = rownum
FROM (
SELECT seq, row_number () OVER (ORDER BY seq) rownum
FROM Table
WHERE no = @no
) UpdateTarget