sql query to save data in data base

static MySqlConnection connection;
        public void Add(Test test)
        {
            openConnection();
            string query = "INSERT INTO Math (dateTime,degree,testTime) VALUES('" + String.Format("{0:yyyy-M-d HH:mm:ss}", test.DateTime) + "','" + test.Degree + "','" + test.TestTime + "')";
            MySqlCommand cmd = new MySqlCommand(query, connection);
            cmd.ExecuteNonQuery();
            closeConnection();
        }
        private void openConnection()
        {
            try
            {
                connection = new MySqlConnection("SERVER=" + server + ";" + "DATABASE=" + database + ";" + "UID=" + username + ";" + "PASSWORD=" + password + ";");
                connection.Open();
                Isconnected = true;
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
                Isconnected = false;
            }
        }
        private void closeConnection()
        {
            try
            {
                connection.Close();
                Isconnected = false;
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }