Question

I have a Table with these columns

- ProjectId
 - Generation
 - Expected 
 - CarryOver

I am trying to update my already populated table in this fashion:

  Generation = Integral Part of ((Generation + CarryOver of Previous Row)/10 )
  CarryOver =  decimal part of  ((Generation + CarryOver of Previous Row)/10 )

where Previous Row and Current Row both have same projectId

Below is the query am using to achieve this:

UPDATE TTable 

SET 

TTable.Expected=(TTable.Generation+ ISNULL(STable.CarryOver,0)),
TTable.CarryOver =(TTable.Generation+ISNULL(STable.CarryOver,0))-CONVERT(INT,(TTable.Generation+ISNULL(STable.CarryOver,0)))

FROM
(
    SELECT ROW_NUMBER()OVER(order by ProjectId,MonthYear) as RowNumber,ProjectId, 
    [MonthYear],[Month],[Generation],[Expected],[CarryOver]
    FROM #SRECEsimated 
)TTable,

(
    SELECT ROW_NUMBER()OVER(order by ProjectId,MonthYear) as RowNumber,ProjectId,
        [MonthYear],[Month],[Generation],[Expected],[CarryOver] 
    FROM #SRECEsimated 
) STable


Where   
TTable.RowNumber  = STable.RowNumber+1 AND
TTable.ProjectId = STable.ProjectId 

….but something strange happens, update happens only for first two rows. For other rows,
ISNULL(STable.CarryOver,0) returns 0. why??
Please help me. or suggest some other way to achieve this

EDIT: on running the query

ProjectId   MonthYear   Month   Year    Generation  Expected    CarryOver
10  2011-10-01 00:00:00.000 10  2011    56.748             56            0.748
10  2011-11-01 00:00:00.000 11  2011    12.004             12            0.752
10  2011-12-01 00:00:00.000 12  2011    10.632             10            0.632
10  2012-01-01 00:00:00.000 01  2012    11.928             11            0.928
10  2012-02-01 00:00:00.000 02  2012    7.580               7            0.580
100 2011-12-01 00:00:00.000 12  2011    5.897               5            0.897
100 2012-01-01 00:00:00.000 01  2012    0.881               1            0.778

data is generated as shown above. notice how the logic doesn’t work after 3row

Original Ouput. Before running the update query:

ProjectId   MonthYear   Month   Year    Generation  Expected    CarryOver
10  2011-10-01 00:00:00.000 10  2011    56.748            56             0.748
10  2011-11-01 00:00:00.000 11  2011    12.004            NULL           NULL
10  2011-12-01 00:00:00.000 12  2011    10.632            NULL           NULL
10  2012-01-01 00:00:00.000 01  2012    11.928            NULL           NULL
10  2012-02-01 00:00:00.000 02  2012    7.580             NULL           NULL
100 2011-12-01 00:00:00.000 12  2011    5.897             5           0.897
100 2012-01-01 00:00:00.000 01  2012    0.881             NULL           NULL

Answer 1

The following query will give you the expected results

(Test code https://gist.github.com/1969171 for those that want to play)

PID Date       M  Y    Generation  Expected CarryOver   
10  2011-10-01 10 2011 56.748      56       0.748
10  2011-11-01 11 2011 12.004      12       0.752
10  2011-12-01 12 2011 10.632      11       0.384
10  2012-01-01 01 2012 11.928      12       0.312
10  2012-02-01 02 2012 7.58        7        0.892
100 2011-12-01 12 2011 5.897       5        0.897
100 2012-01-01 01 2012 0.881       1        0.778

---

DECLARE rowItems CURSOR FOR 
SELECT ProjectId, [Month], [Year], Generation FROM TTable
ORDER BY ProjectId,[Year] ,CAST([Month] as int)

DECLARE @p int, @m VARCHAR(5), @y int, @g FLOAT, @priorP int, 
        @carryOver FLOAT, @expected FLOAT

OPEN rowItems

FETCH NEXT FROM rowItems INTO @p, @m, @y, @g

SET @priorP = -1
SET @carryOver = 0.0

WHILE @@FETCH_STATUS = 0
BEGIN

   IF NOT @p = @priorP SET @carryOver = 0.0

   SET @expected = @g+@carryOver
   SET @carryOver = ROUND(@expected-FLOOR(@expected),3,0)   

   UPDATE TTable
     SET EXPECTED = FLOOR(@expected), CarryOver = @carryOver
   WHERE  ProjectId = @p and [Month] = @m and  [Year] = @y

   SET @priorP = @p

   FETCH NEXT FROM rowItems INTO @p, @m, @y, @g

END

CLOSE rowItems
DEALLOCATE rowItems

SELECT * FROM TTable

You need to do this in a loop. The query you use is getting the original value of the carry over column not the updated value.