อยากทราบเรื่องการ Auto ID ผมใช้ V C# กับ ฐาน ข้อมูล Access 2003

private void Form1_Load(object sender, EventArgs e)
        {
            {
                string conStr = "Provider=Microsoft.Jet.OleDb.4.0;" +
                    "Data Source=" + Application.StartupPath +
                    @"\DB1.mdb";
                _conn = new OleDbConnection(conStr);
                _conn.Open();
                
            }
        }
        private void Form1_FormClosing(object sender, FormClosedEventArgs e)
        {
            _conn.Close();
        }
        private void GenerateID()
        {

        private void fillID()
        {
            readData();
            string textid = "";
            int rowindex = _dataset.Tables["rep"].Rows.Count;
            if (rowindex == 0)
            { textid = "AT10001"; }
            else
            {
                textid = _dataset.Tables["rep"].Rows[0]["ATID"].ToString();
                textid = textid.Substring(2);
                int Addid = 0; Addid = Convert.ToInt32(textid);
                textid = "AT" + (Addid + 1);
            }
            textBox1.Text = textid;
           
        }
        private void readData()
        {
            string sql = "SELECT * FROM Repair";
            _command = new OleDbCommand(sql, _conn);

            OleDbDataAdapter adapter = new OleDbDataAdapter(_command);
            _dataset = new DataSet();
            adapter.Fill(_dataset, "rep");
            _rowCount = _dataset.Tables["rep"].Rows.Count;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            fillID();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            string txtid = "";
            if (textBox1.Text == ""){MessageBox.Show("Plz insert ID");
            
                return;
            }
            string sql = "INSERT INTO Repair(ATID, CustomerName)" +
                         "VALUES (@at, @cust)";
            _command = new OleDbCommand(sql, _conn);

            _command.Parameters.AddWithValue("at", textBox1.Text);
            _command.Parameters.AddWithValue("cust", textBox2.Text);

            int d = _command.ExecuteNonQuery();
            if (d < 1)
            {
                toolStripStatusLabel1.Text = "ERROR";
                return;
            }
            else
            {
                toolStripStatusLabel1.Text = "Complete";
            }
            clearBindings();
        }

        private void btnClear_Click(object sender, EventArgs e)
        {
            if (btnClear.Text == "Clear")
            {
                clearBindings();


            }
            else
            {
                btnClear.Text = "Clear";


                bindings();
            }
        }
        private void clearBindings()
        {
            for (int i = 0; i < groupBox1.Controls.Count; i++)
            {
                if (groupBox1.Controls[i] is TextBox)
                {
                    TextBox tbx = (TextBox)groupBox1.Controls[i];
                    tbx.Text = "";
                    tbx.DataBindings.Clear();
                }


            }

        }
        private void bindings()
        {
            textBox1.DataBindings.Add("Text", _dataset, "rep.ATID");
            textBox2.DataBindings.Add("Text", _dataset, "rep.CustomerName");
        }

    }
}