---

using System.Data.SqlClient;

private void button1_Click(object sender, EventArgs e)
{
    string login = textBox1.Text;
    string password = textBox2.Text;

    string connStr = @"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=|DataDirectory|\WindowsFormsApp5.mdf;Integrated Security=True";

    using (SqlConnection conn = new SqlConnection(connStr))
    {
        conn.Open();

        string query = "SELECT Role FROM Users WHERE Login=@login AND Password=@password";

        SqlCommand cmd = new SqlCommand(query, conn);
        cmd.Parameters.AddWithValue("@login", login);
        cmd.Parameters.AddWithValue("@password", password);

        var result = cmd.ExecuteScalar();

        if (result != null)
        {
            string role = result.ToString();

            if (role == "Admin")
            {
                Admin form = new Admin();
                form.Show();
            }
            else
            {
                Guest form = new Guest();
                form.Show();
            }

            this.Hide();
        }
        else
        {
            MessageBox.Show("Неверный логин или пароль");
        }
    }
}