PHP - Update Based On Calculated Field

       $tablesum ++;
        $guestsum += $row->reservation_pax;
<?php echo $guestsum;?>&nbsp;&nbsp;<?php echo _guest_summary;?>

<!-- Begin reservation table data -->
<br/>
<table class="global resv-table-small" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
		
		<?php
		echo "<td class='noprint'> </td>";
		echo "<td>Time</td>";
		echo "<td>Guests/Type</td>";
		echo "<td>Name</td>";
		echo "<td>Special Instructions/Notes</td>";
		echo "<td class='noprint'>Table</td>";
		echo "<td class='noprint'>Status</td>";
		echo "<td class='noprint'>Created</td>";
		echo "<td class='noprint'>Details/Delete</td>";

	echo "</tr>";
		
		// Clear reservation variable
		$reservations ='';
		
		if ($_SESSION['page'] == 1) {
			$reservations =	querySQL('all_reservations');
		}else{
			$reservations =	querySQL('reservations');
		}
		
		// reset total counters
		$tablesum = 0;
		$guestsum = 0;
			
		if ($reservations) {
			
			//start printing out reservation grid
			foreach($reservations as $row) {
				// reservation ID
				$id = $row->reservation_id;
				$_SESSION['reservation_guest_name'] = $row->reservation_guest_name;
				// check if reservation is tautologous
				$tautologous = querySQL('tautologous');
				
			echo "<tr id='res-".$id."'>";
			echo "<td";
			// daylight coloring
			if ($row->reservation_time > $daylight_evening){
				echo " class='evening noprint'";
			}else if ($row->reservation_time > $daylight_noon){
				echo " class='afternoon noprint'";
			}else if ($row->reservation_time < $daylight_noon){
				echo " class='morning noprint'";
			}
			
			echo " style='width:10px !important; padding:0px;'>&nbsp;</td>";
			echo "<td id='tb_time'";
			// reservation after maitre message
			if ($row->reservation_timestamp > $maitre['maitre_timestamp'] && $maitre['maitre_comment_day']!='') {
				echo " class='tautologous' title='"._sentence_13."' ";
			}
			echo ">";
			echo "<strong>".formatTime($row->reservation_time,$general['timeformat'])."</strong></td>";
			echo "<td id='tb_pax'><strong class='big'>".$row->reservation_pax."</strong>&nbsp;&nbsp;<span class='noprint'>";
			printType($row->reservation_hotelguest_yn);
				//echo "<img src='images/icons/user-silhouette.png' class='middle'/>";
			echo "</span></td><td style='width:10%' id='tb_name'><span class='noprint'>".printTitle($row->reservation_title)."</span><strong> <a id='detlbuttontrigger' href='ajax/guest_detail.php?id=".$id."'"; 
			// color guest name if tautologous
			if($tautologous>1){echo" class='tautologous tipsy' title='"._tautologous_booking."'";}
			echo ">".$row->reservation_guest_name."</a></strong>";
			
			// old reservations symbol
			if( (strtotime($row->reservation_timestamp) + $general['old_days']*86400) <= time() ){
				echo "<img src='images/icons/clock-bolt.png' class='help tipsyold middle smicon' title='"._sentence_11."' />";
			}
			// recurring symbol
			if ($row->repeat_id !=0) {
	            echo "&nbsp;<img src='images/icons/loop-alt.png' alt='"._recurring.
					 "' title='"._recurring."' class='tipsy' border='0' >";
	        }
	
			echo"</td><td style='width:10%' id='tb_note'>";
				if ($_SESSION['page'] == 1) {
			 		echo $row->outlet_name;
			 	}else{
					echo $row->reservation_notes;
				}
			echo "</td>";
			
			if($_SESSION['wait'] == 0){
				echo "<td class='big tb_nr' style='width:85px;' id='tb_table'><img src='images/icons/table_II.png' class='tipsy leftside noprint' title='"._table."' /><div id='reservation_table-".$id."' class='inlineedit'>".$row->reservation_table."</div></td>";
			}
			echo "<td class='noprint'><div>";
				getStatusList($id, $row->reservation_status);
			echo "</div></td>";
			echo "<td class='noprint'>";
			echo "<small>".$row->reservation_booker_name." | ".humanize($row->reservation_timestamp)."</small>";
			echo "</td>";
			echo "<td class='noprint'>";
			// MOVE BUTTON
			//	echo "<a href=''><img src='images/icons/arrow.png' alt='move' class='help' title='"._move_reservation_to."'/></a>";
			
			// WAITLIST ALLOW BUTTON
			if($_SESSION['wait'] == 1){
				$leftspace = leftSpace(substr($row->reservation_time,0,5), $availability);
				if($leftspace >= $row->reservation_pax && $_SESSION['outlet_max_tables']-$tbl_availability[substr($row->reservation_time,0,5)] >= 1){	    
					echo"&nbsp;<a href='#' name='".$id."' class='alwbtn'><img src='images/icons/check-alt.png' name='".$id."' alt='"._allow."' class='help' title='"._allow."'/></a>&nbsp;&nbsp;";
				}
			}
			// EDIT/DETAIL BUTTON
			echo "<a href='?p=102&resID=".$id."'><img src='images/icons/pen-fill.png' alt='"._detail."' class='help' title='"._detail."'/></a>&nbsp;&nbsp;";
			// DELETE BUTTON
			if ( current_user_can( 'Reservation-Delete' ) && $q!=3 ){
		    	echo"<a href='#modalsecurity' name='".$row->repeat_id."' id='".$id."' class='delbtn'>
					<img src='images/icons/delete.png' alt='"._cancelled."' class='help' title='"._delete."'/></a>";
			}
		echo"</td></tr>";
		$tablesum ++;
		$guestsum += $row->reservation_pax;
			}
		}
		?>
	</tbody>
	<tfoot>

		<tr style="border:1px #000;">
			<td class=" noprint"></td><td></td>
			<td colspan="2" class="bold"><?php echo $guestsum;?>&nbsp;&nbsp;<?php echo _guest_summary;?></td>
			<td></td>
			<td colspan="2" class="bold"><?php echo $tablesum;?>&nbsp;&nbsp;<?php echo _tables_summary;?></td>
			<?php
			if($_SESSION['wait'] == 0){
				//echo "<td></td>";
			}
			?>
		</tr>
	</tfoot>
</table>
<!-- End reservation table data -->

            <form class="form-horizontal" action="update.php?idnumber=<?php echo $idnumber?>" method="post">
                <?php
                    // Connect to Store_Name (sn) table to get values for dropdown
                    $pdo = Database::connect();
                    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
                    $sql = "SELECT DISTINCT store_name FROM store_master ORDER BY store_name ASC";
                    $q_sn = $pdo->prepare($sql);
                    $q_sn->execute();
                    $count_sn = $q_sn->rowCount();        
                    $result_sn = $q_sn->fetchAll();
                    Database::disconnect();

                    // Connect to Item_Description (id) table to get values for dropdown                    
                    $pdo = Database::connect();
                    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
                    $sql = "SELECT DISTINCT product_name FROM product_master ORDER BY product_name ASC";
                    $q_id = $pdo->prepare($sql);
                    $q_id->execute();
                    $count_id = $q_id->rowCount();        
                    $result_id = $q_id->fetchAll();
                    Database::disconnect();

                    foreach($fields AS $field => $attr){
                        $current_store_name = $values['store_name'];
                        $current_item_description = $values['item_description'];
                        
                        //Print the form element for the field.
                        if ($field == 'store_name')
                            {
                                echo $current_store_name;
                                echo '<br />';
                                echo $current_item_description;
                            
                                echo '<div class="control-group">';
                                    echo "<label class='control-label'>{$attr['label']}: </label>";
                                    echo '<div class="controls">';                            
                                        //Echo the actual input. If the form is being displayed with errors, we'll have a value to fill in from the user's previous submission.
                                        echo '<select class="store-name" name="store_name">';                                            
                                            // echo '<option value="">Please select...</option>';
                                            foreach($result_sn as $row)
                                                {
                                                    echo "<option value='" . $row['store_name'] . "'>{$row['store_name']}</option>";
                                                }
                                                // $row['store_name'] = $current_store_name;
                                        echo "</select>";

                                    echo '</div>';
                                echo '</div>';
                            }
                        elseif ($field == 'item_description')
                            {
                                echo '<div class="control-group">';
                                    echo "<label class='control-label'>{$attr['label']}: </label>";
                                    echo '<div class="controls">';                            
                                        echo '<select class="item-desc" name="item_description">';
                                            // echo '<option value="">Please select...</option>';
                                            foreach($result_id as $row)
                                                {
                                                    echo "<option alue='" . $row['product_name'] . "'>{$row['product_name']}</option>";
                                                }    
                                        echo "</select>";
                                    echo '</div>';
                                echo '</div>';                                        
                            }
                        else
                            {
                                echo '<div class="control-group">';
                                    echo "<label class='control-label'>{$attr['label']}: </label>";
                                    echo '<div class="controls">';                            
                                        //Echo the actual input. If the form is being displayed with errors, we'll have a value to fill in from the user's previous submission.
                                        echo '<input type="text" name="'.$field.'"' . (isset($values[$field]) ? ' value="'.$values[$field].'"' : '') . ' /></label>';                            
                                    echo '</div>';
                                echo '</div>';                                        
                            }

    $fields = array(
        'store_name'         => array('label' => 'Store Name',
                                     'error' => 'Please enter a store name'),
        'item_description'     => array('label' => 'Item Description',
                                     'error' => 'Please enter an item description'),
        'qty_pkg'             => array('label' => 'Qty / Pkg',
                                     'error' => 'Please indicate whether it\'s Qty or Pkg'),
        'pkg_of'             => array('label' => 'Pkg. Of',
                                     'error' => 'Please enter the quantity'),
        'price'             => array('label' => 'Price',
                                     'error' => 'Please enter the price'),
        'flyer_page'         => array('label' => 'Flyer Page #',
                                     'error' => 'Please enter the flyer page #'),
        'limited_time_sale' => array('label' => 'Limited Time Sale',
                                     'error' => 'Please enter the days for limited-time-sale'),
        'nos_to_purchase'     => array('label' => 'No(s) to Purchase',
                                     'error' => 'Please enter the No. of items to purchase')
    );    
 
...
...
....
        {
            // If [submit] isn't clicked - and therfore POST array is empty - perform a SELECT query to bring in
            // existing values from the table and display, to allow for changes to be made
            $pdo = Database::connect();
            $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
            $sql = "SELECT * FROM shoplist where idnumber = ?";
            $q = $pdo->prepare($sql);
            $q->execute(array($idnumber));
            $values = $q->fetch(PDO::FETCH_ASSOC);

            if(!$values)
                {
                    $error = 'Invalid ID provided';
                }        
            Database::disconnect();
        }

if( $stmt = $db_connect->prepare('UPDATE '.C_T_DRAGONS.' AS d, '.C_T_USERS.' AS u SET d.'.$prop.' = d.'.$prop.'+'.$val.', u.ap=u.ap-1 WHERE d.id = ? AND (SELECT u2.ap FROM '.C_T_USERS.' as u2 WHERE u2.id = ?) > 100') )

UPDATE dragons AS d, users AS u SET d.claws_dam = d.claws_dam+1, u.ap=u.ap-1 WHERE d.id = ? AND (SELECT u2.ap FROM users as u2 WHERE u2.id = ?) > 100

Error : (1093) Table 'd' is specified twice, both as a target for 'UPDATE' and as a separate source for data