-- EmployeeSalesSummary_EmpSalesYearOverYear

SELECT      C.FirstName + ' ' + C.LastName AS Employee, 
            DATEPART(Year,  SOH.OrderDate) AS OrderYear, 
            DATEPART(Month, SOH.OrderDate) AS OrderMonthNum, 
            DATENAME(Month, SOH.OrderDate) AS OrderMonth, 
            SUM(SOD.LineTotal)             AS Sales

FROM        Sales.SalesOrderHeader  SOH 
INNER JOIN  Sales.SalesOrderDetail  SOD ON SOH.SalesOrderID    = SOD.SalesOrderID 
INNER JOIN  Sales.SalesPerson       SP  ON SOH.SalesPersonID   = SP.BusinessEntityID 
INNER JOIN  HumanResources.Employee E   ON SP.BusinessEntityID = E.BusinessEntityID 
INNER JOIN  Person.Person           C   ON E.BusinessEntityID  = C.BusinessEntityID

WHERE       (DATEPART(Year,  SOH.OrderDate) <= @ReportYear - 1 OR
             DATEPART(Year,  SOH.OrderDate)  = @ReportYear     AND 
             DATEPART(Month, SOH.OrderDate) <= @ReportMonth)   
AND         (SOH.SalesPersonID = @EmpID)

GROUP BY    C.FirstName + ' ' + C.LastName, 
            SOH.SalesPersonID, 
            DATEPART(Year,  SOH.OrderDate), 
            DATEPART(Month, SOH.OrderDate), 
            DATENAME(Month, SOH.OrderDate)