gistfile1.php

<?php
	
	$db = new PDO("mysql:dbname=mydb;host=localhost", $user, $password);
	$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

	function get_row($parent_id)
	{
		global $db; //I would normally never do this, but its simpler than explaining the concept of a singleton

		$parent_id = (int) $parent_id; //Cast to int
		
		$q = $db->prepare("
				SELECT 
					posts.post_topic, posts.post_content, posts.post_id, posts.post_date, posts.file_uploaded, 
					posts.post_by, posts.post_parent, users.user_id, users.user_name, users.user_pic 
				FROM 
					posts 
					LEFT JOIN users ON posts.post_by = users.user_id 
				WHERE 
					posts.topic_id = :parent_id
		");

		$q->execute(
			array(
				':parent_id' => $parent_id
			)
		);

		while($row = $q->fetch(PDO::FETCH_OBJ))
		{
			if($row->parent_id != NULL)
			{
				get_row($row->parent_id);
			}

			//Do other shit with $row here
		}
	}	
?>