, CASE WHEN t.OrderMonth IS NULL THEN 'Grand Total' ELSE CAST(t.OrderMonth AS VARCHAR(20)) END b

, t.MonthlySales

, MAX(t.cum_total) cum_total

FROM (SELECT

YEAR(OrderDate) AS OrderYear,

MONTH(OrderDate) AS OrderMonth,

SUM(SubTotal) AS MonthlySales,

SUM(SUM(SubTotal)) OVER (ORDER BY YEAR(OrderDate), MONTH(OrderDate) ROWS UNBOUNDED PRECEDING) cum_total

FROM Sales.SalesOrderHeader

GROUP BY GROUPING SETS ((YEAR(OrderDate), MONTH(OrderDate)))) t

GROUP BY GROUPING SETS ((t.OrderYear

, t.OrderMonth

, t.MonthlySales), t.OrderYear) ;