Window Functions - Running Total with reset

Question

I am using SQL Server 2012 to build an inventory planning / reorder engine.

I have a bunch of dated transactions, call them credits and debits. I want to do two thi

Answer 1

Ugh, based on your comments, the only thing I can think to do is use a cursor, which I hate doing.

SQL Fiddle

declare @Date date
declare @Qty int
declare @RR int


declare @running int  = 0

declare @results table
(dt date,
 qty int,
 rt int,
 rr int
)

declare C cursor for
select TDate, Qty,
RecommendedReplenish 
from (
    select 
        TDate, 
        Qty,
        -1 * (CASE WHEN Qty < 0 AND SUM(Qty) OVER (ORDER BY TDate ROWS UNBOUNDED     PRECEDING) < 0 
                THEN 
            CASE WHEN Qty >  SUM(Qty) OVER (ORDER BY TDate ROWS UNBOUNDED PRECEDING)     THEN Qty ELSE SUM(Qty) OVER (ORDER                        BY TDate ROWS UNBOUNDED PRECEDING) END
        ELSE 0 END) as RecommendedReplenish
        /* Wrong, does not account for balance resetting to zero */
    from TX 
) T order by TDate

open c
fetch next from c into @date,@qty,@rr
WHILE @@FETCH_STATUS = 0
BEGIN



  set @running = @running + @qty
  if @running <0
    begin
      set @running = 0
    end

  insert into @results values (@date,@qty,@running,@rr)

  fetch next from c into @date,@qty,@rr
end
close c
deallocate c
select
*
from @results

Which as far as I can tell, gives you the desired result. It ain't pretty, I'm sure it could use some cleanup, but it works.

+-------------+------+-----+----+
|     DT      | QTY  | RT  | RR |
+-------------+------+-----+----+
| 2014-03-01  |  20  | 20  |  0 |
| 2014-03-02  | -10  | 10  |  0 |
| 2014-03-03  | -20  |  0  | 10 |
| 2014-03-04  | -10  |  0  | 10 |
| 2014-03-05  |  30  | 30  |  0 |
| 2014-03-06  | -20  | 10  | 10 |
| 2014-03-07  |  10  | 20  |  0 |
| 2014-03-08  | -20  |  0  | 20 |
| 2014-03-09  |  -5  |  0  |  5 |
+-------------+------+-----+----+