namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            List<St> l = new List<St> { 
                new St{Name="A",Num=3,Yue="一月"},
                new St{Name="B",Num=2,Yue="一月"},
                new St{Name="A",Num=5,Yue="一月"},
                new St{Name="B",Num=2,Yue="一月"},
                new St{Name="A",Num=2,Yue="二月"},
                new St{Name="B",Num=1,Yue="二月"},
                new St{Name="A",Num=2,Yue="二月"}
            };


            var q = l.GroupBy(e => new { e.Name, e.Yue })
                .Select(
                     g =>
                         new
                         {
                             客户名称 =g.Key.Name,                            
                             数量 = g.Sum(e => (Int32)(e.Num)),
                             日期 = g.Key.Yue,
                         }
                 );

            foreach (var item in q)
            {
                Console.WriteLine(item.客户名称 + "----" + item.数量 + "----" + item.日期);
            }
        }
    }

    class St
    {
        public string Name { get; set; }
        public int Num { get; set; }
        public string Yue { get; set; }

    }
}

select 客户名称,sum(num) as 数量,日期
from 表 group by 客户名称,日期

SELECT     CONVERT(datetime, CONVERT(varchar(20), dbo.Rec_SalesOrder.AutitDate, 111)) AS AutitDate, SUM(dbo.Rec_SalesOrder_Sub.Quantity) 
                      AS TotleQuantity, dbo.Mer_Package.Barcodes, dbo.Mer_Product.UserCode, dbo.Mer_Product.Name, dbo.Mer_Package.ProductID, 
                      dbo.Rec_SalesOrder.StoresID
FROM         dbo.Rec_SalesOrder INNER JOIN
                      dbo.Rec_SalesOrder_Sub ON dbo.Rec_SalesOrder.ID = dbo.Rec_SalesOrder_Sub.ParentID INNER JOIN
                      dbo.Mer_Package ON dbo.Rec_SalesOrder_Sub.PackageID = dbo.Mer_Package.ID INNER JOIN
                      dbo.Mer_Product ON dbo.Mer_Package.ProductID = dbo.Mer_Product.ID
GROUP BY dbo.Rec_SalesOrder.OrderStatus, dbo.Mer_Package.Barcodes, dbo.Mer_Product.UserCode, dbo.Mer_Product.Name, CONVERT(datetime, 
                      CONVERT(varchar(20), dbo.Rec_SalesOrder.AutitDate, 111)), dbo.Rec_SalesOrder.StoresID, dbo.Mer_Package.ProductID
HAVING      (dbo.Rec_SalesOrder.OrderStatus = 0)