equals两边的参数字段名的大小写必须完全匹配

            var propID = 1;
            var list = from t in tt
                       join detail in OrderDetailList
                       on new { ID = t.ID, PropId = propID } equals new { ID = detail.OrderID, PropId = detail.PropID } into od
                       from dieDetail in od.DefaultIfEmpty()
                       orderby dieDetail.PropValue
                       select t;