C# winform combobox 在绑定数据之后插入一项选择项

/// <summary>
/// 填充comboboxB超医师
/// </summary>
private void setDBPyhNameComboBox()
{
this.combPhy.DataSource = null;
DBConnectioin dbc = new DBConnectioin();
SqlConnection conn = new SqlConnection(DBConnectioin.conStr);
conn.Open();
//DbHelperSQL.setComboList(combPhy, "select PhyID,PhyName  from Physician", "Physician", "PhyName", "PhyID");
string sSQL = "select PhyID,PhyName  from Physician";
string sTable = "Physician";

DataSet dsCourtesy = new DataSet();
SqlDataAdapter daCourtesy = new SqlDataAdapter();
DbHelperSQL.setCommand(dsCourtesy, daCourtesy, sSQL, sTable);
daCourtesy.Fill(dsCourtesy);
combPhy.DataSource = dsCourtesy.Tables[0].DefaultView;
DataRow dr = dsCourtesy.Tables[0].NewRow();
combPhy.DisplayMember = "PhyName";
combPhy.ValueMember = "PhyID";
dr["PhyName"] = "全部";
dr["PhyID"] = -1;
dsCourtesy.Tables[0].Rows.InsertAt(dr, 0);
//combPhy.Text = "全部";

}