I am trying to get meta value from GD Rating table for each post ID with following sql:

$querystr = "SELECT meta_value FROM $wpdb->gdrts_itemmeta WHERE meta_key LIKE 'stars-rating_rating'";
$ratings = $wpdb->get_results($querystr);
foreach ($ratings as $rating)
{
    $rating->meta_value;
}
$ratingku = get_post_meta($post->ID, $rating, true);

But it failed, It return a word: "ARRAY".

How to get meta_value from another table (created by a plugin) for each post by using SQL or Query?