WordPressのWP_Queryでjoin, order byの内容を直接指定する

function my_clauses ( $clauses ) {
    global  $wpdb;
    $clauses["join"] .= " INNER JOIN $wpdb->term_taxonomy ON $wpdb->term_relationships.term_taxonomy_id = $wpdb->term_taxonomy.term_taxonomy_id ";
    $clauses["join"] .= " INNER JOIN $wpdb->terms ON $wpdb->term_taxonomy.term_id = $wpdb->terms.term_id ";
    return $clauses;
}
add_filter( 'posts_clauses', 'my_clauses' );

function my_orderby ( $where = '' ) {
    global  $wpdb;
    $where =  "$wpdb->terms.slug ASC";
    return $where;
}
add_filter( 'posts_orderby', 'my_orderby' );