使用lag()检查TransDate2 天内的变化并将其组合在一起（作为一个段）。之后使用row_number()生成所需的序列

with 
cte as
(
    select *,
           g = case when datediff(day,
                                  lag(t.TransDate) over (order by t.TransDate),
                                  t.TransDate
                                  ) <= 2
                    then 0
                    else 1
                    end
    from   tbl t
),
cte2 as
(
    select *, grp = sum(g) over (order by TransDate)
    from cte
)
select *, row_number() over (partition by grp order by TransDate)
from   cte2 

db<>小提琴演示