how do i add a conditional to a query?

[Antivirus]

Trying to add a conditional to the following query, but can't quite get it to work... any ideas what i am doing wrong?

PHP Code:

$querycontents = $db->query_read("
                        SELECT erc_content.*, erc_contenttype.contenttype
                        FROM erc_content
                        LEFT JOIN erc_contenttype ON erc_content.contentid = erc_contenttype.contenttypeid
                        ");

    if ($_GET['contenttypeid'])
    {
        $querycontents .= " AND erc_content.contenttypeid = '".$_GET['contenttypeid']."'";
    }    
    $querycontents .= " ORDER BY erc_contenttype.displayorder, erc_content.displayorder";