Test code for http://stackoverflow.com/questions/9530693/self-join-to-update-rows-of-the-table/9545830#9545830

953063.sql

CREATE TABLE TTable
    (
            ProjectId INT,
            MonthYear DATETIME, 
            Month VARCHAR(5), 
            Year INT,
            Generation FLOAT,
            Expected FLOAT,
            CarryOver FLOAT
        )
INSERT INTO TTable
VALUES        
    (10,'2011-10-01 00:00:00.000','10',2011,56.748,56,0.748)

INSERT INTO TTable
VALUES        
    (10,'2011-11-01 00:00:00.000','11',2011,12.004,NULL,NULL)

INSERT INTO TTable
VALUES        
    (10,'2011-12-01 00:00:00.000','12',2011,10.632,NULL,NULL)

INSERT INTO TTable
VALUES        
    (10,'2012-01-01 00:00:00.000','01',2012,11.928,NULL,NULL)
INSERT INTO TTable
VALUES        
    (10,'2012-02-01 00:00:00.000','02',2012,7.580,NULL,NULL)
INSERT INTO TTable
VALUES        
    (100,'2011-12-01 00:00:00.000','12',2011,5.897,5,0.897)
INSERT INTO TTable
VALUES        
    (100,'2012-01-01 00:00:00.000','01',2012,0.881,NULL,NULL)

select * from ttable

SELECT * FROM TTable

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)   
 
--   SELECT @p AS ProjectID, @m AS [Month], @y AS [Year], @g AS [Generation],
--       FLOOR(@expected) AS Expected,
--       @carryOver AS CarryOver

   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