private void button3_Click(object sender, EventArgs e)
        {
            ForeignKey f = new ForeignKey(con, comboBox1.SelectedItem.ToString(), foreign, false);

            f.Show();
        }
        private void updateForeign_Click(object sender, EventArgs e)
        {
            ForeignKey f = new ForeignKey(con, comboBox1.SelectedItem.ToString(), foreign.Trim(), true);

            f.Show();
        }