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the following is an example showing the code and queries needed to accomplish this task - <?php // initialization // these settings should be in the php.ini on your system - error_reporting(E_ALL); ini_set('display_errors', '1'); // Start the session session_start(); // fake a logged in user $_SESSION['user_id'] = 1; // insure the current visitor is logged in if(!isset($_SESSION['user_id'])) { // handle a non-logged in user here... header('location:index.php'); die; // stop code execution } // use exceptions for database statement errors and only handle the exception for user recoverable errors // based on the sql syntax error posted, you ARE using exceptions for database statement errors. do yourself a favor and remove all the existing database error handling logic since it is no longer being used and is just cluttering up your code. require 'pdo_connection.php'; $post = []; // array to hold a trimmed working copy of the form data $errors = []; // array to hold user/validation errors // post method form processing if($_SERVER['REQUEST_METHOD'] === 'POST') { // input(s) - gname, this should be the selected user's id - e.g. gid or similar // trim all the input data at once $post = array_map('trim',$_POST); // if any input is an array, use a recursive trim call-back function here instead of php's trim // validate the input data // the selected user's id if($post['gid'] === '') { $errors['gid'] = 'You must select a user'; } else if($post['gid'] == $_SESSION['user_id']) { $errors['gid'] = 'You cannot select yourself'; } else { // find if the selected user exists $sql = "SELECT COUNT(*) FROM users WHERE id=?"; $stmt=$pdo->prepare($sql); $stmt->execute([ $post['gid'] ]); if(!$stmt->fetchColumn()) { // if you see this error, it is either due to a programming mistake or someone submitting data values that are not from your code $errors['gid'] = 'The selected user does not exist'; } } // if no errors, use the data if(empty($errors)) { // since it is doubtful the OP will change what they are doing, the following updates the value in the token column // start transaction $pdo->beginTransaction(); // subtract 1 token from the current user, if they have enough tokens $sql = "UPDATE users SET token=token-1 WHERE token > 0 AND id=?"; $stmt=$pdo->prepare($sql); $stmt->execute([ $_SESSION['user_id'] ]); if($stmt->rowCount()) { // the UPDATE query affected the row, token was > 0 // add 1 token to the recipient user $sql = "UPDATE users SET token=token+1 WHERE id=?"; $stmt=$pdo->prepare($sql); $stmt->execute([ $post['gid'] ]); } else { // the UPDATE query didn't affect the row, token is not > 0 $errors['token'] = "You don't have enough tokens"; } // if you are here, no database errors/exceptions occurred, commit the transaction $pdo->commit(); } // if no errors, success if(empty($errors)) { $_SESSION['success_message'] = "You have successfully gifted a token"; die(header("Refresh:0")); } } // get method business logic - get/produce data needed to display the page $sql = "SELECT id, username FROM users ORDER BY username"; $stmt = $pdo->query($sql); $all_user_data = $stmt->fetchAll(); // html document starts here... ?> <?php // test for, display, and clear any success message if(!empty($_SESSION['success_message'])) { echo "<p>{$_SESSION['success_message']}</p>"; unset($_SESSION['success_message']); } ?> <?php // test for and display any errors if(!empty($errors)) { echo '<p>'.implode('<br>',$errors).'</p>'; } ?> <?php // display the form, repopulating form fields using any data in $post ?> <form method='post'> <select name='gid'> <option value=''>Select a user</option> <option value='234'>An invalid user</option> <?php foreach($all_user_data as $row) { $sel = isset($post['gid']) && $post['gid'] == $row['id'] ? 'selected' : ''; echo "<option value='{$row['id']}' $sel>{$row['username']}</option>"; } ?> </select><br> <input type='submit'> </form> this code renamed the session variable, because many things have 'id's, what exactly is the id stored in the session? uses the much simpler and more modern PDO database extension.

You were advised to use usort(). Your custom function would compare the totals of each pair of records ($a and $b) and return a negative value if $a should sort before $b or positive if $a sorts after $b. (ie total A - total B) $listings = $data['listings']; usort($listings, function($a, $b) { return $a['item_price']['value'] + $a['postage']['price']['value'] - $b['item_price']['value'] - $b['postage']['price']['value']; }); echo '<pre>' . print_r($listings, 1) . '</pre>';