Sorting by Taxonomy in WordPress

orderby_tax_clauses.inc.php

/*	
    Sorting by Taxonomy in WordPress 
    just add this file in your functions.php file
*/

function orderby_tax_clauses( $clauses, $wp_query ) {
	global $wpdb;
    $taxonomies = get_taxonomies();
    foreach ($taxonomies as $taxonomy) {
    	if ( isset( $wp_query->query['orderby'] ) && $taxonomy == $wp_query->query['orderby'] ) {
    	    var_dump($taxonomy);
    		$clauses['join'] .= " LEFT JOIN (
    			SELECT object_id, GROUP_CONCAT(name ORDER BY name ASC) AS $taxonomy
    			FROM $wpdb->term_relationships
    			INNER JOIN $wpdb->term_taxonomy USING (term_taxonomy_id)
    			INNER JOIN $wpdb->terms USING (term_id)
    			WHERE taxonomy = '$taxonomy'
    			GROUP BY object_id
    		) AS energy_terms ON ($wpdb->posts.ID = {$taxonomy}_terms.object_id)";
    		$clauses['orderby'] = "energy_terms.$taxonomy ";
    		$clauses['orderby'] .= ( 'ASC' == strtoupper( $wp_query->get('order') ) ) ? 'ASC' : 'DESC';
    	}
    }
	return $clauses;
}

add_filter( 'posts_clauses', 'orderby_tax_clauses', 10, 2 );