Linq_join的有关问题

  DataTable dtA = new DataTable();        dtA.Columns.Add("id", typeof(int));        dtA.Columns.Add("price", typeof(string));        dtA.Rows.Add(1, "111");        dtA.Rows.Add(2, "222");        dtA.Rows.Add(3, "333");        dtA.Rows.Add(4, "444");        dtA.Rows.Add(5, "555");

  DataTable dtB = dtA.Clone();        dtB.Rows.Add(1, "121");        dtB.Rows.Add(2, "221");        dtB.Rows.Add(3, "331");        dtB.Rows.Add(4, "331");        dtB.Rows.Add(5, "331");        dtB.Rows.Add(6, "331");

 DataTable dtC = dtA.Clone();        dtC.Columns.Add("price_excel");        var query = from a in dtA.AsEnumerable()                    join b in dtB.AsEnumerable()                    on a.Field<int>("id") equals b.Field<int>("id") into g                    from b in g.DefaultIfEmpty()                    select new                    {                        id = a.Field<int>("id"),                        price = a.Field<string>("price"),                        price_excel = b == null ? "None" : b.Field<string>("price")                    };        query.ToList().ForEach(q => dtC.Rows.Add(q.id, q.price, q.price_excel));        gwinfo.DataSource = dtC;        gwinfo.DataBind();

//或许这样写，条理更清晰一点:void Main(){    DataTable dtA = new DataTable();        dtA.Columns.Add("id", typeof(int));        dtA.Columns.Add("price", typeof(string));        dtA.Rows.Add(1, "100");        dtA.Rows.Add(2, "100");         DataTable dtB = dtA.Clone();        dtB.Rows.Add(1, "100");         dtB.Rows.Add(3, "100");     DataTable dtC = dtA.Clone();        dtC.Columns.Add("price_excel");            var leftData=from a in dtA.AsEnumerable()                    join b in dtB.AsEnumerable()                    on a.Field<int>("id") equals b.Field<int>("id") into g                    from b in g.DefaultIfEmpty()                    select new                    {                        id = a.Field<int>("id"),                        price = a.Field<string>("price"),                        price_excel = b == null ? "Null" : b.Field<string>("price")                    };    var rightData=from b in dtB.AsEnumerable()                  where  !dtA.AsEnumerable().Select(a=>a.Field<int>("id")).Contains(b.Field<int>("id"))                  select new                     {                            id = b.Field<int>("id"),                            price = "Null",                            price_excel =b.Field<string>("price")                     };         var query =leftData.Union(rightData); query.ToList().ForEach(q => dtC.Rows.Add(q.id, q.price, q.price_excel));}