Retrieve taxonomy terms in order of their post's post_date

gistfile1.php

<?php

global $wpdb;

$post_types = array( 'my_post_type' );
$taxonomy   = array( 'my_taxonomy' );
$order      = 'DESC';

$sql = "SELECT DISTINCT t.*
	FROM $wpdb->terms AS t
	INNER JOIN $wpdb->term_taxonomy AS tt
		ON t.term_id = tt.term_id
	JOIN $wpdb->term_relationships AS tr
		ON tr.term_taxonomy_id = tt.term_taxonomy_id
	JOIN $wpdb->posts AS p
		ON p.ID = tr.object_id
	WHERE tt.taxonomy IN ( '" . implode( "','", $taxonomy ) . "' )
	AND p.post_type IN ( '" . implode( "','", $post_types ) . "' )
	ORDER BY p.post_date {$order};";

$terms_ordered_by_post_date = $wpdb->get_results( $sql );