SELECT 
    QuotaDate AS Year, 
    DATEPART(QUARTER, QuotaDate) AS Quarter, 
    SalesQuota AS SalesQuota,  
    VAR(SalesQuota) OVER (
        ORDER BY DATEPART(YEAR, QuotaDate), DATEPART(QUARTER, QuotaDate)
    ) AS Variance  
FROM 
    Sales.SalesPersonQuotaHistory  
WHERE 
    BusinessEntityID = 277 
    AND DATEPART(YEAR, QuotaDate) = 2012  
ORDER BY QuotaDate;

