how do fill datagridview combobox column using sql on selection of other datagridview comboboxcolumn, here is my database with two column groupwise & itemwise

dear sir,

how do fill datagridview combobox column using sql on selection of other datagridview comboboxcolumn, here is my database with two column groupwise & itemwise
groupwiseitemwise
CABLE      - LAN CABLE CAT-6
CABLE       -POWER CABLE HEAVY 1.5 MT
CABLE       -VGA CABLE 1.5 M
CONNECTOR-RJ-45
MODEM       -D-LINK MODEM 14.4 MBPS DATA CARD
MODEM       -I-BALL MODEM 7.2 MBPS 3.5G DATA CARD
CABINET       -INTEX CABINET
CPU       -INTEL CORE I5 3RD GEN
CPU       -INTEL CORE I3 3RD GEN
CPU       -INTEL DUALCORE 3RD GEN
RAM       -TRANSCEND DDR3 4GB
RAM       -TRANSCEND DDR3 2GB

and my c# code is as fallows

 private void gdvpurches_SelectionChanged(object sender, EventArgs e)
        {
            try
            {

                cn.Open();

                for (i = 0; i <= gdvpurches.Rows.Count - 2; i++)
                {
                    group = Convert.ToString(gdvpurches.Rows[i].Cells[1].Value);
                    cmd = new SqlCommand("select itemwise from yeeessort where groupwise='" + group + "'", cn);
                    dr = cmd.ExecuteReader();
                    while (dr.Read())
                    {
                        cbitemname.Items.Add(dr[0]);
                        

                    }
                    dr.Close();
                    cbitemname.Items.Clear();
                }
               
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
            finally
            {

                cn.Close();
            }
        }


when i run this code   cbitemname.Items.Add(dr[0]); get filled all itemname of all rows on selection on groupwise field

please help us

thanks....