linq左连接

   Table1和Table2连接，把Table1的全列出来

         var tempData = from a in table1

                           join b  in table2

                           on a.Id equals b.aId

                           into TempTable

                           from temp in TempTable.DefaultIfEmpty()

                           select new

                           {

                               Program = a.UnitOfBusiness,

                               Tier = a.Tier,

                               Market = a.Market,

                               Id = a.Id,

                               CRM = temo.CRM,//表2的内容

                               RMShipId =temp.Id    //表2的内容

                          };
             temp里面的字段就是b(table2)的字段，select表2的字段就要temp点字段，不能用b点字段，b点不来任何字段