DATATABLE中数据如何筛选重复数据

string[] temp = null;

                    sql= "select originalName from DelFileList order by id desc";
                    DataTable tb = db.getTable(sql);
                    if (tb.Rows.Count > 0)
                    {
                        //对重复的数据进行筛选
                        Hashtable ht = new Hashtable();
                        foreach (DataRow dr in tb.Rows)
                        {
                            string s = dr["originalName"];
                            if (!ht.Contains(s))
                                ht[s] = dr["originalName"];
                        }

                        temp = new string[ht.Count];
                        ht.Keys.CopyTo(temp, 0);
                    }