Ristrict GridView Duplicates

Hello Friends,

I m designing an application of a restaurant but I m facing a problem, I want to restrict duplicate values in GridView. For example: I Want if a user select particular item form LISTVIEW twice item will not add but quantity increase.

Note :I m inserting rows in Invoice Table when retrieving rows in Gridview from Items Table;

Please help me, I also attached GUI and Table snaps and sourceCode, Thanks





using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.OleDb;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication8
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        OleDbConnection con;
        OleDbDataAdapter dAdapter;
        OleDbCommandBuilder cBuilder;
        DataTable dTable;
        //DataSet ds;
        OleDbCommand cmd;
        DataView myDataView;
        //string query;
       
        private void button1_Click(object sender, EventArgs e)
        {
            
            
           

            int index = listView1.SelectedItems[0].Index;

         
                con = new OleDbConnection(@"Provider=Microsoft.ACE.Oledb.12.0;Data Source=D:\\gridview.accdb");
                cmd = new OleDbCommand();
                cmd.CommandText = "Select * from ITEMS";

                dAdapter = new OleDbDataAdapter(cmd.CommandText, con);
                dTable = new DataTable();
                cBuilder = new OleDbCommandBuilder(dAdapter);
                cBuilder.QuotePrefix = "[";
                cBuilder.QuoteSuffix = "]";
                myDataView = dTable.DefaultView;
                dAdapter.Fill(dTable);
                dataGridView1.Rows.Add(dTable.Rows[index][0], dTable.Rows[index][1], dTable.Rows[index][2], dTable.Rows[index][3]);

                cmd = new OleDbCommand();
                cmd.CommandText = string.Format("INSERT INTO INVOICE VALUES('{0}','{1}','{2}','{3}')", dataGridView1.Rows[index].Cells[0].Value, dataGridView1.Rows[index].Cells[1].Value, dataGridView1.Rows[index].Cells[2].Value, dataGridView1.Rows[index].Cells[3].Value);
                cmd.Connection = con;
                con.Open();
                cmd.ExecuteNonQuery();
                MessageBox.Show("ORDER DELIVERED");
                con.Close();

           
            


        }

        private void Form1_Load(object sender, EventArgs e)
        {
            DataGridViewTextBoxColumn col = new DataGridViewTextBoxColumn();
            col.HeaderText = "ID";
            col.ValueType = typeof(int);
            dataGridView1.Columns.Add(col);

            col = new DataGridViewTextBoxColumn();
            col.HeaderText = "ITEM";
            col.ValueType = typeof(String);
            dataGridView1.Columns.Add(col);

            col = new DataGridViewTextBoxColumn();
            col.HeaderText = "PRICE";
            col.ValueType = typeof(int);
            dataGridView1.Columns.Add(col);

            col = new DataGridViewTextBoxColumn();
            col.HeaderText = "QTY";
            col.ValueType = typeof(int);
            dataGridView1.Columns.Add(col);
           
        }

      
    }
}