public void login(string login, string password)
        {
            string query = "SELECT COUNT(*) FROM users WHERE Login = login";
            cmd = new MySqlCommand(query, connection);

            int result;

            connection.Open();
            result = Convert.ToInt32(cmd.ExecuteScalar());
            connection.Close();

            if(result > 0)
            {
                query = "SELECT Password FROM users WHERE Login = login";
                cmd = new MySqlCommand(query, connection);

                string result2;

                connection.Open();
                result2 = cmd.ExecuteScalar().ToString();
                connection.Close();

                if(result2 == password)
                {
                    query = "SELECT * FROM users WHERE Login = login";
                    cmd = new MySqlCommand(query, connection);

                    connection.Open();
                    reader = cmd.ExecuteReader();
                    while (reader.Read())
                    {
                        logged = new User();
                        logged.EmployeeNumber = (int)reader["EmployerNumber"];
                        logged.StudentNumber = (int)reader["IndexNumber"];
                        logged.password = (string)reader["Password"];
                        logged.login = (string)reader["Login"];
                        logged.permissions = (string)reader["Permissions"];
                    }
                    connection.Close();

                    if (logged.permissions == "administrator")
                    {
                        AdministationPanel admin = new AdministationPanel();
                        admin.Show();

                    }
                }
                else
                {
                    MessageBox.Show("Niepoprawne hasło");
                }
            }
            else
            {
                MessageBox.Show("Niepoprawna nazwa użytkownika");
            }
        }