private void dataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e)
        {
            string connectionString = "server=127.0.0.1; database=biblioteka; user=zyrc; password=eloelo67";
            MySqlConnection connection = new MySqlConnection(connectionString);
            connection.Open();
            try
            {
                MySqlCommand cmd = connection.CreateCommand();
                cmd.CommandText = "SELECT * FROM ksiazka";
                MySqlDataAdapter adap = new MySqlDataAdapter(cmd);
                DataSet ds = new DataSet();
                adap.Fill(ds);
                dataGridView1.DataSource = ds.Tables[0].DefaultView;
            }
            catch (Exception)
            {
                throw;
            }
            finally
            {
                if (connection.State == ConnectionState.Open)
                {
                    connection.Clone();
                }
            }
        }