不幸的是，SQLServer不支持窗口函数中的日期范围规范。我建议在这里进行横向连接：

select 
    t.*, 
    t1.timestamp last_timestamp, 
    datediff(second, t1.timestamp, t.timestamp) diff_seconds
from mytable t
outer apply (
    select top(1) t1.*
    from mytable t1
    where 
        t1.user_id = t.user_id 
        and t1.timestamp >= dateadd(minute, -3, t.timestamp)
        and t1.timestamp < t.timestamp
    order by t1.timestamp desc
) t1

子查询将在3分钟内为同一行带来最新的行 user_id （或空结果集，如果在该时间段内没有行）。然后可以在外部查询中使用该信息来显示相应的 timestamp ，并计算与当前值的差值。

只需计算当前时间和延迟时间戳的差值，如果超过3分钟，则返回null：

with cte as
 (
   select 
      t.*
     ,datediff(second, timestamp, lag(timestamp) over (partition by user_id order by timestamp) as diff_seconds
   from mytable as t
 )
select cte.*
  ,case when diff_seconds <= 180 then diff_seconds end
from cte