Question

我有两张桌子：

产品和库存

我目前选择产品的内容并对库存表进行第二次调用，以总结产品ID的总库存量，这非常慢。

我想要的是创建对数据库的单个调用以获取Product表的内容，并将stock表中的StockInHand总和（链接到ProductID）的总和如下所示：

如果有人可以告诉我如何成功加入表格并在同一个ProductID的调用中将Stock表的QtyInHand相加，我会非常感激。

我的原始代码：

            var query = from products in data.Products
                        where products.Deleted == false
                        orderby products.FullPath
                        select new
                        {
                            ProductID = products.ProductID,
                            Description = products.Description,
                            Price = products.RetailPrice ?? 0,
>>>> VERY SLOW!             StockLevel = cProducts.GetStockTotalForProduct(products.ProductID), 
                            FullPath = products.FullPath
                        };

            if (query != null)
            {
                dgv.DataSource = query;
            }

我理解我需要加入表格，但我不确定使用LINQ执行此操作的语法：

    var query = 
                from product in data.Products
                join stock in data.ProductStocks on product.ProductID equals stock.ProductID
 DO SOMETHING CLEVER HERE!!
                select new
                {
                    ProductID = product.ProductID,
                    Description = product.Description,
                    Price = product.RetailPrice ?? 0,
                    StockLevel = >>>>>>>> CALL TO THE OTHER TABLE IS VERY SLOW,
                    FullPath = products.FullPath
                };

            if (query != null)
            {
                dgv.DataSource = query;
            }

Answer 1

我认为这应该有效：

 var query = from product in data.Products
                join stock in data.ProductStocks on product.ProductID equals stock.ProductID
                select new
                {
                    ProductID = product.ProductID,
                    Description = product.Description,
                    Price = product.RetailPrice ?? 0,
                    StockLevel = stock.StockLevel,
                    FullPath = products.FullPath
                };

Answer 2

我认为你正在寻找group by来做总和：

var query = from p in data.Products
            join s in data.ProductStocks on p.ProductID equals s.ProductID
            group s by p into g
            select new {
                ProductID = g.Key.ProductID,
                Description = g.Key.Description,
                Price = g.Key.Price ?? 0,
                FullPath = g.Key.FullPath,
                StockLevel = g.Sum(s => s.StockInHand)
            };

SQL连接表和SUM值

2 个答案: