//Estriamo i dati per scalare i piani conto e sapere a quale cliente riferirsi
                                query = "SELECT iva, totale, cliente FROM vendite WHERE id=" + System.Convert.ToInt32(dataGridView1.CurrentRow.Cells[0].Value);
                                oleCmd = new MySqlCommand(query, conn);
                                oleCmd.Transaction = trans;
                                reader = oleCmd.ExecuteReader();

                                int idCliente;
                                decimal iva, totale;

                                while (reader.Read())
                                {
                                    idCliente = System.Convert.ToInt32(reader[2]);
                                    iva = System.Convert.ToDecimal(reader[0]);
                                    totale = System.Convert.ToDecimal(reader[1]);
                                }
                                reader.Close();


 for (int j = 0; j < _totNC.Count; j++)
                                {
                                    //Piano conti cliente
                                    query = "UPDATE piano_conti_clienti SET avere=avere-?totale WHERE id_cliente=" + idCliente + " AND Year(data)=" + ((DateTime)_annoNC[j]).Year;
                                    oleCmd = new MySqlCommand(query, conn);
                                    oleCmd.Transaction = trans;
....