生成工单时序列号重复

Question

我正在尝试在成功预订后生成条形码门票，并且运行良好。但昨天(2017年1月6日)晚上11点59分，一名客户预订了2张门票，但门票sl.no重复。那就是两张票都是1。实际上应该是2。但是下一个客户的票证sl.no是正确的，它是3,4,5。在下面生成票证的代码中是否有任何错误？

for($j=1;$j<=$cat_array[$i];$j++) {
  $sel_max_dt =  mysql_query("select MAX(DT) AS maxdt, MAX(REC_NO) AS maxrec FROM  tkt_barcode");
  //to select max date and max rec no.
  $row_max_dt = mysql_fetch_array($sel_max_dt);
  $dt_max = $row_max_dt['maxdt'];
  //$no_max = $row_max_dt['maxno'];
  $recno = $row_max_dt['maxrec'];
  if($dt_max ==  date("Y-m-d") && $recno == $TxnID) {
    //if same date and same bkid  barcode slno continues.
    $sel_no = mysql_query("select MAX(BARCODE_SLNO) AS maxno FROM  tkt_barcode WHERE REC_NO=".$TxnID);
    $row_sel_no = mysql_fetch_array($sel_no);   
    $tkt_slno = $row_sel_no['maxno'];
    $tkt_slno = $tkt_slno + 1;
  }
  if($dt_max ==  date("Y-m-d")&& $recno != $TxnID) {
    //if same date and different bkid  barcode slno continues.
    $sel_no = mysql_query("select MAX(BARCODE_SLNO) AS maxno FROM  tkt_barcode WHERE DT='$dt_max' ");
    $row_sel_no = mysql_fetch_array($sel_no);   
    $tkt_slno = $row_sel_no['maxno'];
    $tkt_slno = $tkt_slno + 1;
  }
  if($dt_max != date("Y-m-d") && $recno != $TxnID) {
    //if not same date start barcode slno from 1.
    $tkt_slno = 1;
  }
  $sel_sl_no = mysql_query("select MAX(SL_NO) AS slno FROM  tkt_barcode WHERE REC_NO=".$TxnID);
  $row_slno = mysql_fetch_array($sel_sl_no);
  $slno = $row_slno['slno'];
  $bartkt_slno = $slno + 1;
  if($i==1 && $j>$count_promo_adult && $arr_edit["PROMO_CODE"]!=""){
    //adult cat and total adult count > total promo adult count
    $disc_adult = $adult_amt;
    $discamt=$adult_amt - $disc_adult ; //  discount amt
    $rate=$adult_amt;  //normal rate
    $net_amt=$disc_adult; //discount rate
    $pro_cd ="";
    //promo code is null when total adult count > total promo adult count
   } //end if
  //string pading digits 
  $len_txn =strlen($TxnID); // bookid length 
  $pad = 6; //str_pad digits
  if($len_txn > 5) {
    if($len_txn==6) { $pad = $pad-1;}// if 6 digit
    if($len_txn==7){ $pad = $pad-2;}// if 7 digit
  }
  $fullbar = $TxnID.str_pad($tkt_slno, $pad, 0, STR_PAD_LEFT).$clnd_date.$counter_no;
  //barcode no
  $fields  = "BARCODE_SLNO,DT,FIN_YEAR,Counter_Code,Branch_cd,REC_NO,BARCODE,TICKET_TYPE,CATG_CD,AMT,DISC_AMT,SL_NO,NET_AMT,BCODE_CATG_SLNO,BCODE_SLNO_GEN,BCODE_SLNO_CATG_TOT,DAY_TYPE,Check_in_date,PROMO_CODE,TAX,S_TAX,conv_base_rate,conv_tax_rate";
  $values = "'$tkt_slno','$booked_date','$fin_year','$counter_no','$branch','$TxnID','$fullbar','$cat_name_tkt','$i','$rate','$discamt','$bartkt_slno','$net_amt','$j','$count','$cat_tot','$type_day','$date_check','$pro_cd','$tax_each','$ser_tax_each','$conv_base','$conv_tax'";
  $sql_tkt = $objA->insert_fields(TABLEPREFIX.'tkt_barcode',$fields,$values);
}//end for loop