Dátum alapján összegző (MSSQL)

// https://www.mssqltips.com/sqlservertip/5771/querying-sql-server-tables-from-net/

using System;
using System.Drawing;
using System.Windows.Forms;
using System.Data;
using System.Data.SqlClient;

/*

Form-ra kell 1-1 : button1, textBox1, textBox2, label1

*/

namespace WindowsFormsApp1
{
    public partial class Form1 : Form
    {
        SqlConnection con;
        String conString = @"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=C:\Temp\tesztMSSQLdatabase.mdf;Integrated Security=True;Connect Timeout=30";

        public Form1()
        {
            InitializeComponent();
            textBox1.Multiline = true;
            textBox2.Text = DateTime.Today.ToString("yyyy.MM.dd");
        }

        private void button1_Click(object sender, EventArgs e)
        {
            textBox1.Clear();
            label1.Text = "";

            using (SqlConnection connection = new SqlConnection(conString))
            {
                string queryString = "SELECT datum, osszeg FROM  [dbo].[Kurucz] WHERE datum = @datum";
                SqlCommand command = new SqlCommand(queryString, connection);
                command.Parameters.AddWithValue("@datum", textBox2.Text);
                connection.Open();
                SqlDataReader reader = command.ExecuteReader();
                try
                {
                    while (reader.Read())
                    {
                        textBox1.AppendText(reader["datum"] + "\t" + reader["osszeg"] + "\n");
                    }
                    reader.Close();
                    queryString = "SELECT sum(osszeg) osszesen FROM  [dbo].[Kurucz] WHERE datum = @datum";
                    command = new SqlCommand(queryString, connection);
                    command.Parameters.AddWithValue("@datum", textBox2.Text);
                    label1.Text = command.ExecuteScalar().ToString();

                }
                finally
                {
                    reader.Close();
                }
            }
        }

    }
}