С праздником всех. Что я не так делаю? Почему скрипт не возвращает результат.

<?php
include("user_auth.php");
$user_id = $_COOKIE['viewer_id'];
$tests = $_POST['tests'];

$mysqli = new mysqli($db_host, $db_user, $db_pass, $db_name);
if (!mysqli_connect_errno()) {
if($tests){
$stmt = $mysqli->prepare("SELECT `cabinet`.`name_test`, `a1`.`answer_id` as answer_id, `a2`.`answer_id` as answer_id2 FROM `cabinet` JOIN `answers` a1 ON `a1`.`test_id` = `cabinet`.`test_id` AND `a1`.`user_id` = ? AND `a1`.`friend_id` = ? LEFT JOIN `answers` a2 ON a2.test_id = `cabinet`.`test_id` AND `a2`.`user_id` = ? GROUP BY `answer_id` ORDER BY `a1`.`id`");
$stmt->bind_param('iii', $user_id, $tests, $tests);
$stmt->execute();
$stmt->bind_result($col1, $col2);
while ($stmt->fetch()) {
        echo $col1; 
    } 
$stmt->close(); 
}
}
else {
echo "Не удалось установить подключение к базе данных";
}
?>