C#实现数据库的递归查询

表结构如下：
标识号　　名称　　   上级标识号
mid      mname        mparentid
1        菜单一      0
2        菜单二      1
3        菜单三      1
4        菜单四      2
5        菜单五      3

要用递归程序实现某一标识号（包括本身）下的所有菜单，要实现这个程序，我们这里取出所有符合的菜单标识号，用“，”连接成字符串，实现的方法如下：

/// <summary>
/// 取得菜单下的所有下级菜单
/// </summary>
/// <param name="mid"></param>
/// <param name="Conn"></param>
/// <returns></returns>
public string queryAllMenu(int mid, SqlConnection Conn)
{
 string Result = mid.ToString();
 string cmdSQL = "select mid from t_menu where mparentID =" + mid;
 try
 {
  DataSet ds = new DataSet();
  SqlDataAdapter cmd1 = new SqlDataAdapter(cmdSQL,Conn);
  cmd1.Fill(ds,"Menu");
  DataTable dt = ds.Tables["Menu"];
  for(int i=0; i < dt.Rows.Count; i++)
  {
   int mno = Convert.ToInt32(dt.Rows[i][0].ToString());
   if("".Equals(Result))
    Result += mno;
   else
    Result += "," + mno;
   string sRes = menuChild(mno,Conn);
   if(!"".Equals(sRes))
    Result +=  "," + sRes;
  } 
  if(Conn.State != ConnectionState.Closed)
   Conn.Close();
 }
 catch
 {
  return Result;
 }
 return Result; 
}

private string menuChild(int ParentId, SqlConnection Conn)
{
 string Result = String.Empty;
 string cmdSQL = "select mid from t_menu where mParentID =" + ParentId;
 try
 {
  DataSet ds= new DataSet();
  SqlDataAdapter cmd = new SqlDataAdapter(cmdSQL,Conn);
  cmd.Fill(ds,"downMenu");
  DataTable dt = ds.Tables["downMenu"];
  for(int i=0; i < dt.Rows.Count; i++)
  {
   int mid = Convert.ToInt32(dt.Rows[i][0].ToString());
   if("".Equals(Result))
  Result += mid;
   else
  Result += "," + mid;
   Result += menuChild(mid, Conn);
  }
  if(Conn.State != ConnectionState.Closed)
   Conn.Close();
 }
 catch
 {
  return Result;
 }
 return Result;
}