private void AddButton_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                int    id     = Convert.ToInt32(ID_tb.Text);
                int    client = Convert.ToInt32(Client_tb.Text);
                int    abon   = Convert.ToInt32(Abon_tb.Text);
                string start  = Start_tb.Text;
                string end    = End_tb.Text;

                string        connectionString = @"Data Source =.\SQLEXPRESS; Initial Catalog = FitnessCenter; Integrated Security = True";
                SqlConnection connection       = new SqlConnection(connectionString);
                connection.Open();
                string     cmdTxt  = $"INSERT INTO AbonnementsSales (ID_card, ID_client, ID_abonnement, StartDate, EndDate) VALUES ('{id}', '{client}', '{abon}',  '{start}',  '{end}')";
                SqlCommand command = new SqlCommand(cmdTxt, connection);
                int        number  = command.ExecuteNonQuery();
                MessageBox.Show("Изменения сохранены успешно!\nВставлено объектов: " + number, "Статус действия", MessageBoxButton.OK, MessageBoxImage.Information);

                ID_tb.Clear(); Client_tb.Clear(); Abon_tb.Clear(); Start_tb.Clear(); End_tb.Clear();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "ERROR!", MessageBoxButton.OK, MessageBoxImage.Error);
            }
        }
        private void ChangeButton_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                int    id     = Convert.ToInt32(ID_tb.Text);
                int    client = Convert.ToInt32(Client_tb.Text);
                int    abon   = Convert.ToInt32(Abon_tb.Text);
                string start  = Start_tb.Text;
                string end    = End_tb.Text;

                int    newid     = Convert.ToInt32(NewID_tb.Text);
                int    newclient = Convert.ToInt32(NewClient_tb.Text);
                int    newabon   = Convert.ToInt32(NewAbon_tb.Text);
                string newstart  = NewStart_tb.Text;
                string newend    = NewEnd_tb.Text;


                string        connectionString = @"Data Source =.\SQLEXPRESS; Initial Catalog = FitnessCenter; Integrated Security = True";
                SqlConnection connection       = new SqlConnection(connectionString);
                connection.Open();

                string     cmdTxt1  = $"UPDATE AbonnementaSales SET ID_client = '{newclient}'  WHERE ID_card = '{id}'";
                SqlCommand command1 = new SqlCommand(cmdTxt1, connection);
                string     cmdTxt2  = $"UPDATE AbonnementsSales SET ID_abonnement = '{newabon}'  WHERE ID_card = '{id}'";
                SqlCommand command2 = new SqlCommand(cmdTxt2, connection);
                string     cmdTxt3  = $"UPDATE AbonnemensSales SET StartDate = '{newstart}'  WHERE ID_card = '{id}'";
                SqlCommand command3 = new SqlCommand(cmdTxt3, connection);
                string     cmdTxt4  = $"UPDATE AbonnemensSales SET EndDate = '{newend}'  WHERE ID_card = '{id}'";
                SqlCommand command4 = new SqlCommand(cmdTxt4, connection);


                command1.ExecuteNonQuery(); command2.ExecuteNonQuery(); command3.ExecuteNonQuery(); command4.ExecuteNonQuery();
                MessageBox.Show("Изменения сохранены успешно!", "Статус действия", MessageBoxButton.OK, MessageBoxImage.Information);


                ID_tb.Clear(); Client_tb.Clear(); Abon_tb.Clear(); Start_tb.Clear(); End_tb.Clear();
                NewID_tb.Clear(); NewClient_tb.Clear(); NewAbon_tb.Clear(); NewStart_tb.Clear(); NewEnd_tb.Clear();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "ERROR!", MessageBoxButton.OK, MessageBoxImage.Error);
            }
        }
        private void DeleteButton_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                int id = Convert.ToInt32(ID_tb.Text);

                string        connectionString = @"Data Source =.\SQLEXPRESS; Initial Catalog = FitnessCenter; Integrated Security = True";
                SqlConnection connection       = new SqlConnection(connectionString);
                connection.Open();
                string     cmdTxt  = $"DELETE FROM AbonnementsSales WHERE ID_card = '{id}'";
                SqlCommand command = new SqlCommand(cmdTxt, connection);
                int        number  = command.ExecuteNonQuery();
                MessageBox.Show("Изменения сохранены успешно!\nУдалено объектов: " + number, "Статус действия", MessageBoxButton.OK, MessageBoxImage.Information);

                ID_tb.Clear(); Client_tb.Clear(); Abon_tb.Clear(); Start_tb.Clear(); End_tb.Clear();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "ERROR!", MessageBoxButton.OK, MessageBoxImage.Error);
            }
        }