/************************************** tabPage 1 **************************************/
        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (comboBox1.SelectedIndex == 0)
            {
                ds  = new DataSet();
                oda = new OracleDataAdapter("select * from store_products order by id_product", oc);
                oda.Fill(ds);
                dataGridView1.DataSource = ds.Tables[0];
                Products.printDataGridTitle(dataGridView1);
            }
            if (comboBox1.SelectedIndex == 1)
            {
                ds  = new DataSet();
                oda = new OracleDataAdapter("select * from store_clients order by id_client", oc);
                oda.Fill(ds);
                dataGridView1.DataSource = ds.Tables[0];
                Clients.printDataGridTitle(dataGridView1);
            }
            if (comboBox1.SelectedIndex == 2)
            {
                ds  = new DataSet();
                oda = new OracleDataAdapter("select * from store_distributors order by id_distrib", oc);
                oda.Fill(ds);
                dataGridView1.DataSource = ds.Tables[0];
                Distributors.printDataGridTitle(dataGridView1);
            }
            if (comboBox1.SelectedIndex == 3)
            {
                ds  = new DataSet();
                oda = new OracleDataAdapter("select * from store_bookings order by id_booking", oc);
                oda.Fill(ds);
                dataGridView1.DataSource = ds.Tables[0];
                Bookings.printDataGridTitle(dataGridView1);
            }
        }
// add distributor
        private void button5_Click(object sender, EventArgs e)
        {
            if (textBox23.Text != "" && textBox24.Text != "")
            {
                Distributors distributor = new Distributors(System.Convert.ToInt32(textBox22.Text),
                                                            textBox23.Text,
                                                            System.Convert.ToInt32(textBox24.Text));
                distributor.addDistributor();
            }
            int newID = System.Convert.ToInt32(textBox22.Text);

            ++newID;
            textBox22.Text = newID.ToString();
            textBox23.Text = "";
            textBox24.Text = "";
        }
/************************************** tabPage 2 **************************************/
        private void tabPage2_Enter(object sender, EventArgs e)
        {
            ds  = new DataSet();
            oda = new OracleDataAdapter("select * from store_products order by name_pr", oc);
            oda.Fill(ds);
            dataGridView2.DataSource = ds.Tables[0];
            Products.printDataGridTitle(dataGridView2);

            ds  = new DataSet();
            oda = new OracleDataAdapter("select * from store_distributors order by title", oc);
            oda.Fill(ds);
            dataGridView3.DataSource = ds.Tables[0];
            Distributors.printDataGridTitle(dataGridView3);

            textBox12.Text    = DateTime.Today.ToString();
            textBox12.Enabled = false;

            textBox9.Enabled = true;
            textBox9.Text    = "";
            textBox14.Text   = "";
        }