SELECT isnull(c.Name, '') "Nazwa", isnull(CAST(YEAR(sod.ModifiedDate) AS NCHAR), '') "Rok",
CAST(round(100 * SUM(sod.LineTotal) /
(SUM(SUM(sod.LineTotal)) OVER(partition BY c.ProductCategoryID)), 2) AS DECIMAL(10,2)) "Procent"
FROM Sales.SalesOrderDetail sod JOIN Production.Product p ON sod.ProductID = p.ProductID
JOIN Production.ProductSubcategory sc ON p.ProductSubcategoryID = sc.ProductSubcategoryID
JOIN Production.ProductCategory c ON sc.ProductCategoryID = c.ProductCategoryID
WHERE c.Name = 'Bikes'
GROUP BY GROUPING sets((c.Name, YEAR(sod.ModifiedDate), c.ProductCategoryID), ())
;