C#Mysql行无法验证

我想验证MySQL数据库中的二维码。但是二维码是无效的，我想进入我的程序

如何验证它

if (decodeStr == null) 
{
    MessageBox.Show("There is no QR Code!");
} 
else 
{
    player.Play();

    ConnectToDatabase();
    MySqlCommand cmd = new MySqlCommand("Select Name, LPN From visitors Where password = @password;", conn);
    cmd.Parameters.AddWithValue("@password", decodeStr);

    MySqlDataReader reader = cmd.ExecuteReader();
    while (reader.Read()) 
    {
        if(reader["password"].ToString() == decodeStr){
            //this is the problem here..
        }
        MessageBox.Show("he");

        name = reader["Name"].ToString();
        lpn = reader["LPN"].ToString();
    }

    CheckForIllegalCrossThreadCalls = false;
    //reader.Close();
    videoStream.Stop();
    this.Hide(); // closes the Form2 instance.
    Application.Run(new VisitorData());

}

---

尝试下面的代码：将您的连接字符串放入此代码中

if (decodeStr == null)
            {
                MessageBox.Show("There is no QR Code!");
            }
            else
            {
                player.Play();

                MySqlConnection connection;
                string cs = @"server=server ip;userid=username;password=userpass;database=databse";
                connection = new MySqlConnection(cs);
                connection.Open();

                MySqlCommand command = new MySqlCommand();
                string SQL = "Select Name, LPN From visitors Where password = @password";
                command.CommandText = SQL;
                command.Parameters.Add("@password", decodeStr);
                command.Connection = connection;
                command.ExecuteNonQuery();
                connection.Close();
                var reader = command.ExecuteReader();
                while (reader.Read())
                {
                    MessageBox.Show("he");

                    name = reader["Name"].ToString();
                    lpn = reader["LPN"].ToString();
                }

                CheckForIllegalCrossThreadCalls = false;
                //reader.Close();
                videoStream.Stop();
                this.Hide(); // closes the Form2 instance.
                Application.Run(new VisitorData());

            }

---

尝试下面的代码：将您的连接字符串放入此代码中

if (decodeStr == null)
            {
                MessageBox.Show("There is no QR Code!");
            }
            else
            {
                player.Play();

                MySqlConnection connection;
                string cs = @"server=server ip;userid=username;password=userpass;database=databse";
                connection = new MySqlConnection(cs);
                connection.Open();

                MySqlCommand command = new MySqlCommand();
                string SQL = "Select Name, LPN From visitors Where password = @password";
                command.CommandText = SQL;
                command.Parameters.Add("@password", decodeStr);
                command.Connection = connection;
                command.ExecuteNonQuery();
                connection.Close();
                var reader = command.ExecuteReader();
                while (reader.Read())
                {
                    MessageBox.Show("he");

                    name = reader["Name"].ToString();
                    lpn = reader["LPN"].ToString();
                }

                CheckForIllegalCrossThreadCalls = false;
                //reader.Close();
                videoStream.Stop();
                this.Hide(); // closes the Form2 instance.
                Application.Run(new VisitorData());

            }

---

验证标准是什么？哪个变量是QR码？能否成功连接数据库？decodeStr是存储QR码的变量。我想显示错误消息，如果mySQLyes数据库中没有数据，我可以连接，验证标准是什么？哪个变量是QR码？能否成功连接数据库？decodeStr是存储QR码的变量。如果mySQLyes数据库中没有可以连接的数据，我想显示错误消息，但我想在我的sql连接中进行验证。因为所有二维码都有值。但是数据库中只有一些qrcode匹配。但是我想在我的sql连接中进行验证。因为所有二维码都有值。但数据库中只有一些qrcode匹配。