wp - get list of dates for posts with selected term

<?php
// Vladimir Zhelnov // neatek.ru // neatek.pw
// functions.php (Wordpress)
function get_archive_date($date = '', $before = false, $term = 0) {
    global $wpdb;
    $res = array();
    if(!empty(strtotime($date))) {
        $date = date('Y-m-d H:i:s' ,strtotime($date));
        if($before) {
            $x = '<';
        }
        else {
            $x = '>';
        }
        $sql = "SELECT year(post_date) FROM ".$wpdb->posts."";
        if($term > 0) {
            $sql .= " INNER JOIN ".$wpdb->term_relationships."
                ON ".$wpdb->posts.".ID = ".$wpdb->term_relationships.".object_id
                WHERE
                `term_taxonomy_id`='".$term."'";
        }
        $sql .= "AND `post_status`='publish'
        AND `post_type` <>'attachment'
        AND post_date ".$x." '".$date."'
        GROUP by year(post_date)
        ORDER by year(post_date) DESC";
        $res = $wpdb->get_col($sql);
    }
    return $res;
}