Execute the following script in Query Editor to demonstrate the usage of cursor for running total generation. Generally this solution performs better than applying correlated subquery.

USE AdventureWorks

ALTER TABLE Sales.SalesOrderHeader

  ADD CumulativeTotal MONEY NOT NULL

  CONSTRAINT dfSalesOrderHeader DEFAULT(0)

go --

SET NoCount ON

DECLARE

  @SalesOrderID INT,

  @TotalDue MONEY,

  @CumulativeTotal MONEY

SET @CumulativeTotal = 0

  -- 1) set up the cursor     

  DECLARE cRun CURSOR FAST_FORWARD

    FOR

      SELECT SalesOrderID, TotalDue

        FROM Sales.SalesOrderHeader

        ORDER BY OrderDate, SalesOrderID

   -- 2) open the cursor

  OPEN cRun

  FETCH cRun INTO @SalesOrderID, @TotalDue  -- prime the cursor

  WHILE @@Fetch_Status = 0

    BEGIN

      SET @CumulativeTotal = @CumulativeTotal + @TotalDue

      UPDATE Sales.SalesOrderHeader

        SET CumulativeTotal = @CumulativeTotal

        WHERE SalesOrderID = @SalesOrderID   

      FETCH cRun INTO @SalesOrderID, @TotalDue  -- fetch next

    END

  CLOSE cRun

  DEALLOCATE cRun

go --

SELECT SalesOrderID, TotalDue, CumulativeTotal

  FROM Sales.SalesOrderHeader

  ORDER BY OrderDate, SalesOrderID

go --

ALTER TABLE Sales.SalesOrderHeader

  DROP CONSTRAINT dfSalesOrderHeader

ALTER TABLE Sales.SalesOrderHeader

  DROP COLUMN CumulativeTotal