สอบถามปัญหาการกรอกข้อมูลใน textbox เมื่อประกาศขายสินค้า เพราะเป็น PK เลยกรอกซ้ำกันไม่ได้อาจจะให้กรอกซ้ำกันได้

protected void bttsell_Click(object sender, EventArgs e)
        {
           
            using (SqlConnection con = new SqlConnection(sportsecondhandConnectionString))
            {
                con.Open();



                int imagelen = FileUpload1.PostedFile.ContentLength;
                byte[] picbyte = new byte[imagelen];
                FileUpload1.PostedFile.InputStream.Read(picbyte, 0, (imagelen));

            using (SqlTransaction transaction = con.BeginTransaction())
                {

                    if (Page.IsValid)
                        {

                    try
                    {
                 
                        string sql = "INSERT INTO CustomerUser(Username,Userphone,UserIdentification) VALUES(@Username,@Userphone,@UserIdentification)";
                            SqlParameter[] prms = new SqlParameter[3];
                            prms[0] = new SqlParameter("@Username", SqlDbType.VarChar, 50);
                            prms[0].Value = txtnamesell.Text.Trim();
                            prms[1] = new SqlParameter("@Userphone", SqlDbType.VarChar, 50);
                            prms[1].Value = txtphonenumber.Text.Trim();
                            prms[2] = new SqlParameter("@UserIdentification", SqlDbType.VarChar, 50);
                            prms[2].Value = txtidcard.Text.Trim();


                            using (SqlCommand cmd = new SqlCommand(sql, con))
                            {
                                cmd.Transaction = transaction;
                                cmd.Parameters.AddRange(prms);
                                cmd.ExecuteNonQuery();

                            }



                            sql = "INSERT INTO ProductSecondHand(Productname,Productprice,Productdetail,Productpic,Useremail,Productdate,Producteditdate,Ipaddress,browserversion,Producttype,UserIdentification) VALUES(@Productname,@Productprice,@Productdetail,@Productpic,@Useremail,@Productdate,@Producteditdate,@Ipaddress,@browserversion,@Producttype,@UserIdentification)";
                            SqlParameter[] prms1 = new SqlParameter[11];
                            prms1[0] = new SqlParameter("@Productname", SqlDbType.VarChar, 50);
                            prms1[0].Value = txtnameproduct.Text.Trim();
                            prms1[1] = new SqlParameter("@Productprice", SqlDbType.Money);
                            prms1[1].Value = txtpriceproduct.Text.Trim();
                            prms1[2] = new SqlParameter("@Productdetail", SqlDbType.VarChar, 255);
                            prms1[2].Value = txtdetail.Text.Trim();
                            prms1[3] = new SqlParameter("@Productpic", SqlDbType.Image);
                            prms1[3].Value = picbyte;
                            prms1[4] = new SqlParameter("@Productdate", SqlDbType.DateTime);
                            prms1[4].Value = txtdatetime.Text.Trim();
                            prms1[5] = new SqlParameter("@Producteditdate", SqlDbType.DateTime);
                            prms1[5].Value = txtupdatedate.Text.Trim();
                            prms1[6] = new SqlParameter("@Ipaddress", SqlDbType.VarChar, 50);
                            prms1[6].Value = txtipaddress.Text.Trim();
                            prms1[7] = new SqlParameter("@browserversion", SqlDbType.VarChar, 50);
                            prms1[7].Value = txtbrowser.Text.Trim();
                            prms1[8] = new SqlParameter("@Producttype", SqlDbType.VarChar, 50);
                            prms1[8].Value = ddltypeproduct.Text.Trim();
                            prms1[9] = new SqlParameter("@Useremail", SqlDbType.VarChar, 50);
                            prms1[9].Value = txtemail.Text.Trim();
                            prms1[10] = new SqlParameter("@UserIdentification", SqlDbType.VarChar, 50);
                            prms1[10].Value = txtidcard.Text.Trim();

                            using (SqlCommand cmd1 = new SqlCommand(sql, con))
                            {
                                cmd1.Transaction = transaction;
                                cmd1.Parameters.AddRange(prms1);
                                cmd1.ExecuteNonQuery();

                            }
                           
                            transaction.Commit();
                            con.Close();

                            Result1.Text = "Save Successfully";
                            
                          
                        }
                       
                       
                    
                    catch (Exception ee)
                    {
                        transaction.Rollback();
                        Result1.Text = "Save error" + ee.ToString();
                        
                    }