Select DatePart(yyyy,SaleDate) AS Year,DatePart(MM,SaleDate) AS MM,
SUM(QTY) AS SumQTY From Table1 Where DatePart(yyyy,SaleDate)='2008'
Group by DatePart(yyyy,SaleDate),DatePart(MM,SaleDate)
Union All
Select DatePart(yyyy,SaleDate) AS Year,DatePart(MM,SaleDate) AS MM,
SUM(QTY)*-1 AS SumQTY From Table1 Where DatePart(yyyy,SaleDate)='2007'
Group by DatePart(yyyy,SaleDate),DatePart(MM,SaleDate)