Get WordPress Most Popular Posts By Total Comments

<?php
function popularPosts($num) 
{
	global $wpdb;
 
	$posts = $wpdb->get_results("SELECT comment_count, ID, post_title FROM $wpdb->posts ORDER BY comment_count DESC LIMIT 0 , $num");
 
	foreach ($posts as $post) 
	{
		$id = $post->ID;
		$title = $post->post_title;
		$count = $post->comment_count;
 
		if ($count != 0) 
		{
			$popular .= '<li>';
			$popular .= '<a href="' . get_permalink($id) . '" title="' . $title . '">' . $title . '</a> ';
			$popular .= '</li>';
		}
	}
	return $popular;
}
?>

<div id="tab_popularPosts">
	<ul>
		<?php echo popularPosts(10); ?>
	</ul>
</div>