//Line to Sql 写法
 var data = (from a in Items

             group a by new { a.GroupId, a.Id } into b

             //orderby new ComparerItem() { GroupId = b.Key.GroupId, Id = b.Key.Id } descending
　　　　      .where(o => o.Id>1000)

             select new

              {

                 GroupId = b.Key.GroupId,

                 Id = b.Key.Id,

                 Count = b.Sum(c => c.Count),

                 Weight = b.Sum(c => c.Weight)

               }).OrderBy(t => t.GroupId).ThenBy(t => t.Id);

//labmda 写法

var data = items.GroupBy( t=> t.GroupBy,t=> t.Id)

        .where( f=> f.Id>)

        .Select( g=> new

            {

                GroupId = g.GroupId,

                Id = g.Id,

                Count = g.Count( ),

                SumWeight = g.Sum( x=>x.Weight)

            }

        );

//多表写法

from a in TableA

    join b in TableB on a.Id equals b.aId

    where ((b.Type ==  || b.Type ==  || b.Type == ) && b.State == )

    group new { a.Id, b.Name,b,CreateDate } by new { a.Id, b.Name } into g

    select (new Class1 { Id = g.Key.Id, Name = g.Key.Name ?? "" });  

class Class1

{

    public int Id { get; set; }

    publid string Name { get; set; }

}

from c in Customers

    join p in Purchases

    on c.ID equals p.CustomerID

    group p.Price by new

    {

    p.Date.Year,

    c.Name

    }

    into salesByYear

        orderby salesByYear.Key.Year descending

    select new

        {

        TotalPrice= salesByYear.Sum(),

        Year=salesByYear.Key.Year,

        Name=salesByYear.Key.Name

    }