c# MySqlCommand.ExecuteNonQuery() return 1

I'm trying to execute a SQL request in C# to know if a user is already registered on my data base. To do that, I'm using the following source code :

    public bool pseudoDispo(string pseudo)
    {
        // Ouverture de la connexion SQL
        this.OpenConnection();

        // Création d'une commande SQL en fonction de l'objet connection
        MySqlCommand cmd = this.connection.CreateCommand();
        cmd.CommandText = "SELECT COUNT(*) FROM `user` WHERE `pseudo` = '" + pseudo + "'";

        int test = cmd.ExecuteNonQuery();
        MessageBox.Show(test.ToString());

        // Exécution de la commande SQL
        if (cmd.ExecuteNonQuery() == 1)
        {
            this.connection.Close();
            MessageBox.Show("Registered");
            return true;
        }
        else
        {
            this.connection.Close();
            MessageBox.Show("Not Registered");
            return false;
        }
    }

But the problem is that MySqlCommand.ExecuteNonQuery() always returns -1 and I don't know why. My request seems work because it returns me the good result (1 if registered, 0 if not) on phpmyadmin.

Is there anyone to help me and explain me what I'm doing wrong please?

Thanks!

Edit: I've been trying to do my function on another way by using ExecuteScalar() but now I got some troubles with it because it always returns me 0. I clearly do not understand something but I don't even know what... Can I get more informations about ExecuteScalar() and that kind of functions? I tried to cast it into a string, and it seems that cmd requests an Int64. So I updated my code like that, but it still doesn't work. I'm pretty depressed with my lack of knowledge but anyway, here is the code :

    public int pseudoDispo(string pseudo)
    {
        Int64 dispo_pseudo = 0;
        string sql = "SELECT COUNT(*) FROM `user` WHERE `pseudo` = '[pseudo] = ?' ";

        MySqlCommand cmd = new MySqlCommand(sql);
        try
        {
            this.OpenConnection();

            OleDbCommand dbcommand = new OleDbCommand(sql);

            dbcommand.Parameters.AddWithValue("@p1", pseudo);
            dbcommand.CommandType = CommandType.Text; 

            dispo_pseudo = (Int64)dbcommand.ExecuteScalar();

        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
        }
        return (int)dispo_pseudo;
    }