DATATABLE中数据如何筛选重复数据

string[] temp = null;//存放已经入库的影片路径
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);
}