using(SqlConnection con = new SqlConnection("server=localhost;uid=sa;pwd=sa;database=DemoDB;"))
{
      con.Open();
      string strSQL = "select 另外一个字段,编码字段 from 你的表名";
      SqlDataAdapter adapter = new SqlDataAdapter(strSQL,con);
      DataSet ds= new DataSet();
      adapter.Fill(ds);
      this.DropDownList1.DataSource = ds;
      this.DropDownList1.DataTextField = "另外一个字段";
      this.DropDownList1.DataValueField = "编码字段";
      this.DropDownList1.DataBind();
}