$ wpdb-> get_results无效

i write following code to copy values from one table to another table but $wpdb->get_results not returning anything.

function rating_convert() {
    global $wpdb;
    $likes = $wpdb->get_results('SELECT * FROM ' . $wpdb->prefix . 'up_down_comment_vote_totals', ARRAY_N);
    foreach ($likes as $like) {
        $wpdb->query('UPDATE ' . $wpdb->prefix  . 'comment_rating SET ck_rating_up = ' . $like['vote_count_up'] . ' WHERE ck_comment_id = ' . $like['comment_id']);
        $wpdb->query('UPDATE ' . $wpdb->prefix  . 'comment_rating SET ck_rating_down = ' . $like['vote_count_down'] . ' WHERE ck_comment_id = ' . $like['comment_id']);
    }
}

i have tested every line with echo function.foreach line not running and i think $wpdb->get_results is wrong. please help me. Sorry for my bad english.

i solve this. my table have 147,308 rows. problem is table rows number. i add LIMIT code for only get 1000 rows and remove every row after copy to another table.thanks.

function comment_rating() {
    global $wpdb;
    $likes = $wpdb->get_results('SELECT * FROM ' . $wpdb->prefix . 'up_down_comment_vote_totals LIMIT 0, 1000', ARRAY_A);
    foreach ($likes as $like) {
    echo "id " . $like['comment_id'] . "<br>";
    $wpdb->query('UPDATE ' . $wpdb->prefix  . 'comment_rating SET ck_rating_up = ' . $like['vote_count_up'] . ' WHERE ck_comment_id = ' . $like['comment_id']);
    $wpdb->query('UPDATE ' . $wpdb->prefix  . 'comment_rating SET ck_rating_down = ' . $like['vote_count_down'] . ' WHERE ck_comment_id = ' . $like['comment_id']);
    $wpdb->query('DELETE FROM ' . $wpdb->prefix  . 'up_down_comment_vote_totals WHERE comment_id =  ' . $like['comment_id']);
    }
}