---

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.7.2" />
    </startup>
 <connectionStrings>
    <add 
      name="DefaultCon" 
      connectionString="Data Source=localhost\SQLExpress;Initial Catalog=Exam;Integrated Security=True;TrustServerCertificate=True" 
      providerName="System.Data.SqlClient"/>
  </connectionStrings>
</configuration>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Configuration;

namespace WindowsFormsApp1
{
    internal static class Program
    {
        /// <summary>
        /// Главная точка входа для приложения.
        /// </summary>
        public static string conStr = ConfigurationManager.ConnectionStrings["DefaultCon"].ConnectionString;
        [STAThread]
        static void Main(string[] args)
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
    }
}

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using static System.Windows.Forms.VisualStyles.VisualStyleElement;

namespace WindowsFormsApp1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void LoadDataToGrid(string query, SqlParameter[] parameters = null, string tableName = "Results")
        {
            try
            {
                using (SqlConnection con = new SqlConnection(Program.conStr))
                {
                    con.Open();
                    using (SqlCommand cmd = new SqlCommand(query, con))
                    {
                        if (parameters != null)
                            cmd.Parameters.AddRange(parameters);

                        using (SqlDataReader reader = cmd.ExecuteReader())
                        {
                            DataTable table = new DataTable(tableName);
                            table.Load(reader);
                            table_gv.DataSource = table;
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show($"Ошибка: {ex.Message}\n\nЗапрос:\n{query}");
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string query = @"
                SELECT dbo.Лекарства.Наименование, dbo.Поставки.Количество - dbo.Продажи.Количество AS Остаток FROM dbo.Лекарства INNER JOIN
                dbo.Поставки ON dbo.Лекарства.[Номер лекарства] = dbo.Поставки.[Номер лекарства] INNER JOIN
                dbo.Продажи ON dbo.Лекарства.[Номер лекарства] = dbo.Продажи.[Номер лекарства] GROUP BY dbo.Лекарства.Наименование, dbo.Поставки.Количество - dbo.Продажи.Количество";
            LoadDataToGrid(query);
        }

        private void button2_Click(object sender, EventArgs e)
        {
            string query = @"
                SELECT dbo.Поставщики.Название AS [Наименование поставщика], dbo.Лекарства.Наименование AS [Наименование лекарства] FROM dbo.Лекарства INNER JOIN
                         dbo.Поставки ON dbo.Лекарства.[Номер лекарства] = dbo.Поставки.[Номер лекарства] INNER JOIN
                         dbo.Поставщики ON dbo.Поставки.[Номер поставщика] = dbo.Поставщики.[Номер поставщика] WHERE (dbo.Поставщики.Название = @SupplierName)";

            SqlParameter param = new SqlParameter("@SupplierName", SqlDbType.NVarChar)
            {
                Value = textBox1.Text.Trim()
            };

            LoadDataToGrid(query, new[] { param });
        }

        private void button3_Click(object sender, EventArgs e)
        {
            string query = @"SELECT TOP (3) dbo.Лекарства.Наименование, dbo.Продажи.Количество FROM dbo.Лекарства INNER JOIN dbo.Продажи ON dbo.Лекарства.[Номер лекарства] = dbo.Продажи.[Номер лекарства] ORDER BY dbo.Продажи.Количество DESC";
            LoadDataToGrid(query);
        }
    }
}