string place_class_sql = "select DISTINCT stringsub(car_fee_hostname,1,2) FROM car_park_fee where car_fee_flag = 2";现在报错"dl_fee_place.DisplayMember = "car_fee_hostname";"  

string place_class_sql = "select DISTINCT car_fee_hostname FROM car_park_fee where car_fee_flag = 2";
SqlConnection place_conn = new SqlConnection(fee_conn.sql_conn());
DataSet complace = new DataSet();
place_conn.Open();
SqlDataAdapter myplace = new SqlDataAdapter(place_class_sql, class_conn);
myplace.Fill(complace, "ds");
place_conn.Close();
DataRow dw = complace.Tables[0].NewRow();
dw["car_fee_hostname"] = "全部收费口";
complace.Tables[0].Rows.InsertAt(dw,0);
dl_fee_place.DisplayMember = "car_fee_hostname";
this.dl_fee_place.DataSource = complace.Tables[0];
dl_fee_place.SelectedIndex = 0;

select distinct SUBSTRING(car_fee_hostname,1,3) as car_fee_hostname from