Execute the following script in Query Editor calculate running total without using a loop. In the update statement double assignment is applied.

USE tempdb;

SELECT * INTO POH from AdventureWorks2008.Purchasing.PurchaseOrderHeader

ORDER by PurchaseOrderID

-- select * from POH

ALTER TABLE POH ADD RunningTotal money

GO

SET NOCOUNT ON

GO

DECLARE @RunningTotal MONEY

SET @RunningTotal=0

UPDATE POH

SET @RunningTotal = RunningTotal = @RunningTotal+ISNULL(TotalDue, 0)

GO

SELECT * FROM POH

GO