我有下面的select语句，它应该返回按姓氏排序的记录集，而不是。我已经检查了姓氏字段中是否有空白字符/空格，因为它们都是使用$last_name=trim（filter_input（input_post，'lastname'，filter_sanitize_string））修剪的；。

$query_PaidOrders = "SELECT * FROM `orders` WHERE `payment_received` = '1'";
$rs_PaidOrders=$conn->query($query_PaidOrders);

if($rs_PaidOrders === false){
    trigger_error('SQL error:'.$query_PaidOrders.' Error: '.$conn->error, E_USER_ERROR);
}
else{
  while ($row_PaidOrders=$rs_PaidOrders->fetch_assoc()) {
    $PaidOrderId=$row_PaidOrders['order_id'];
    $query_select_events = "SELECT customers.last_name AS LASTNAME,
                        customers.first_name AS FIRSTNAME,
                        order_details.member_id AS MEMBERID,
                        order_details.event_type AS EVENTTYPE,
                        order_details.event_distance AS EVENTDISTANCE, 
                        order_details.keep_stats AS KEEPSTATS
                        FROM `order_details`

 LEFT OUTER JOIN customers ON order_details.member_id = customers.customer_id 

WHERE order_details.event_id = '$eid' AND order_details.counted_for_discount='1' AND order_details.ORDERNUM = '$PaidOrderId' ORDER BY LASTNAME ASC";

       $rs_events=$conn->query($query_select_events);

       if($rs_events === false){
       trigger_error('SQL error:'.$query_select_events.' Error: '.$conn->error, E_USER_ERROR);
       }
       else{
            while($row_order_details=$rs_events->fetch_assoc()){
      $NAME = $row_order_details['LASTNAME'].", ".$row_order_details['FIRSTNAME'];  
      $member_id=$row_order_details['MEMBERID'];
      $event_type=$row_order_details['EVENTTYPE'];
      $event_distance=$row_order_details['EVENTDISTANCE'];
      $keep_stats=$row_order_details['KEEPSTATS'];
            ?>
            <tr>
               <td><?php echo "$NAME";?></td>
                etc...

我的结果是：b…，h…，h…，s…，b…，r。。。。
我真的被这个难住了。任何帮助都将不胜感激。