SQL上一记录查询

Question

我有以下表格：

+---------+-----------+----------------+---------------------+
|TravLotID|TravLineNum|ProjectCycleTime|    CapacityValue    |
+---------+-----------+----------------+---------------------+
|  14405  |    1      |     60         | 2011-03-16 16:00:00 |  
|  14405  |    2      |     90         |                     |
+---------+-----------+----------------+---------------------+

我想添加一个名为FordwardSchdDate的新字段 对于第一行，它应将ProjectCycleTime值添加到CapacityValue。然后累积结果。

例如，这里应该是什么结果：

+---------+-----------+----------------+---------------------+---------------------+
|TravLotID|TravLineNum|ProjectCycleTime|   CapacityValue     | FordwardSchdDate    |
+---------+-----------+----------------+---------------------+---------------------+
|  14405  |      1    |      60        | 2011-03-16 16:00:00 | 2011-03-16 17:00:00 |  
|  14405  |      2    |      90        |                     | 2011-03-16 18:30:00 |
+---------+-----------+----------------+---------------------+---------------------+

我需要帮助思考如何实现这一目标的逻辑。这是我到目前为止所拥有的

( CASE WHEN TravLineNum = 1
   THEN dbo.fn_DateAdjustWorkingDaysOnly(0 - wt.ProjectedCycleTime, wt.CapacitySlotDateTimeValue)
   ELSE  ' '--dbo.fn_DateAdjustWorkingDaysOnly (wt.ProjectedCycleTime + wt.ParentMinutes, wt.SchdDate)
   END ) AS ForwardSchdDate,

有什么建议吗？谢谢！