[C#] รบกวนถามผู้รู้หน่อยคร๊ เกี่ยวกับการลบ data ที่ซ้ำกัน

protected void btn_Submit_Click(object sender, EventArgs e)
        {
            DataTable Export = gridRolesDataSourceAssetTable();
            //objConnExport.Open();
            foreach (DataRow item in Export.Rows)
            {
                try
                {
                    string strSQLHistory = "INSERT INTO MsOrder  VALUES ('" + item[0] +
                                                                             "','" + item[1] +
                                                                             "','" + item[2] +
                                                                             "','" + item[3] +
                                                                             "','" + item[4] +
                                                                             "','" + item[5] +
                                                                             "','" + item[6] +
                                                                             "','" + item[7] +
                                                                             "','" + item[8] +
                                                                             "','" + item[9] +
                                                                             "','" + item[10] +
                                                                             "','" + item[11] +
                                                                             "','" + item[12] +
                                                                             "','" + item[13] +
                                                                             "','" + item[14] +
                                                                             "','" + item[15] +
                                                                             "','" + item[16] +
                                                                             "','" + item[17] +
                                                                             "','" + item[18] +
                                                                             "','" + item[19] +
                                                                             "','" + item[20] +
                                                                             "','" + item[21] +
                                                                             "','" + item[22] +
                                                                             "','" + item[23] +
                                                                             "','" + item[24] +
                                                                             "','" + item[25] +
                                                                             "','" + item[26] +
                                                                             "','" + item[27] +
                                                                             "','" + item[28] +
                                                                             "','" + item[29] +
                                                                             "','" + hf_EmpCode.Value +
                                                                             "','" + DateTime.Now +
                                                                            "')";

                    SQLService.InsertData(strSQLHistory);

                    ClearData();
                  
                    ScriptManager.RegisterStartupScript(this.Page, Page.GetType(), "text", "Success();", true);

                }
                catch (Exception ee)
                {
                    ScriptManager.RegisterStartupScript(this.Page, Page.GetType(), "text", "Unsuccess();", true);
                }
            }

        }