uCommerce uses a SP called uCommerce_GetProductTop10 to generate the Top 10 product overview found in the backend.

If you are looking for a more flexible solution i think you maybe could get some inspiration from a method i once wrote, to rank products:

 public static IOrderedEnumerable<Ranking> RankPassedProducts(List<string> skus)
        { 
            var validOrders = PurchaseOrder.All().Where(x => x.CompletedDate != null).ToList();
            var validOrderLines = validOrders.SelectMany(y => y.OrderLines);


            var rankingList = new List<Ranking>();
            foreach (var sku in skus)
            {
                var buys = validOrderLines.Where(x => x.Sku == sku).ToList().Sum(y => y.Quantity);
                var newRanking = new Ranking() { Buys = buys, Sku = sku };
                rankingList.Add(newRanking);

            }
            var outputList = rankingList.OrderByDescending(y => y.Buys);
            return outputList;

        }

It takes some time, so i made a caching layer to speed things up.

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