如何基于SQL Server中的先前行创建两个新列？

Question

Suppose I have this table(sort by the Date ):

  Hours Amount Date
1 2     20     1
2 1     20     3
3 6     20     10
4 3     20     20

And I want to create two new columns. Something like this

  Hours Amount Start End Time
1 2     20     20    18  1
2 1     20     18    17  3
3 6     20     17    11  10
4 3     20     11    7   20

Start :

the first Start is the first Amount ,

the next one is based on the first Amount - Hours

and so on

End is basically the next row for Start

Is there a way to do this?

Answer 1

You can use a running sum to do this. Then a lag to get the previous end on to the current row.

select t.*,coalesce(lag(end) over(order by date),start) as start
from (select hours,amount,date,amount-sum(hours) over(order by date) as end
      from tbl
      ) t

Answer 2

Simply subtract the Running Total of those hours from the Amount:

select t.*
  ,amount - cumulative_hours as end
  ,amount - cumulative_hours + hours as start
from
 (
   select hours
     ,amount
     ,date
     ,sum(hours) over(order by date rows unbounded preceding) as cumulative_hours
   from tab
  ) t