mySQL query for getting recent featured images

$attachment_data_list = $wpdb->get_results( $sql );
if ( $attachment_data_list ) {
    foreach ( $attachment_data_list as $attachment_data ) {
        //echo $attachment_data->
        echo '<img src="/photos/wp-content/uploads/';
        echo substr($attachment_data->upload_relative_path,0,-4);
        echo '-88x88.jpg" width="88px" height="88px" class="awesome-thumbnail"/>';
    }
}