var ps = from d in dt.AsEnumerable()

                             join r in re on d.Field<string>("part_no") equals r.IFSID into joinedEmpDept

                             from dept in joinedEmpDept.DefaultIfEmpty() 

                             select new

                                        {

                                            IFSID = d.Field<string>("part_no"),/*从这边开始就报错了*/

                                            Description = d.Field<string>("Description"),

                                            Num = d.Field<decimal>("count_variance"),

                                            Unit = d.Field<string>("unit_meas"),

                                            IN_TRANSIT = d.Field<decimal>("IN_TRANSIT"),

                                            Price = d.Field<decimal>("price"),

                                            MAX = dept.MAX,

                                            MIN = dept.MIN

                                        };

//这样写就不报错

//但是这样写貌似不是左连接，

//dt.AsEnumerable()里面原来有十条数据，用下面的方法只能查询出5条

//既是两个表中都有的5条，另外5条没了

                      var ps = from d in dt.AsEnumerable()