验证用户是否被注册

 protected void btnsumbit_Click(object sender, EventArgs e)
        {
            string connstring = @"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=E:\C#\C#百例\第6章\第98例\EncryptInfo\db\userdb.mdb";
            string Message = String.Empty;
            using (OleDbConnection conn = new OleDbConnection(connstring))
            {
                string sql = "SELECT * FROM [userinfo] WHERE [user_name]='" +txtUser.Text + "' ";
                conn.Open();
                OleDbCommand cmd = new OleDbCommand(sql,conn);
                OleDbDataReader dr = cmd.ExecuteReader();
                if (dr.Read()==false)
                {
                    string InsertSql = "insert  into [userinfo](user_name,user_pwd) values('" + txtUser.Text + "','" + txtPwd.Text + "')";
                    OleDbCommand cmd0 = new OleDbCommand(InsertSql, conn);
                    int q = cmd0.ExecuteNonQuery();
                    if (q > 0)
                    {
                        Message = "注册成功！";
                    }
                    else
                    {
                        Message = "注册失败！";
                    }

                }
                else
                {
                    Message = "该用户名已被注册！";
                }
            }
            Response.Write(Message.ToString());
        }