如何计算页面的meta_key？

Is it possible to count the amount of the same meta_keys for the same post_id.

I have a page with the post_id 44 and every time a user submits something on this page a new database rule is added with the meta_key "post_rating_0".

There are over 30 rules now for this page and I want to count them. For other pages the same thing.

Is this possible?

Code so far:

global $post;
$query_args = array(
            'post_type' => 'page',
            'post_status' => 'publish',
            'posts_per_page' => -1,
            'meta_key' => 'post_rating_0'
            // 'fields' => 'SUM(amount_to_paid)',
        );

$sum = 0;
$query = new WP_Query($query_args);
if ( $query->have_posts() ) {
    while( $query->have_posts() ) {
        $query->the_post();
        // do the processing for each post
        $sum = $sum + intval(get_post_meta(get_the_id(),'post_rating_0', true ));
    }
}
echo $sum ;

This is what I got so far... But what this does is echo the value of "2" what is very logic. It searches for posts with the meta_key "post_rating_0", counts them and that are 2 posts.

What I'm trying to do is count the amount of meta_keys "post_rating_0" are in one page.

This modified code will give you an array with all post_id and the corresponding amount of your specific meta:

$meta_arr = array();
$query = new WP_Query($query_args);
if ( $query->have_posts() ) {
    while( $query->have_posts() ) {
        $query->the_post();
        $post_id = get_the_id();
        $meta_arr[$post_id] = intval(get_post_meta($post_id, 'post_rating_0', false));
    }
}

print_r($meta_arr);

Did some more research and with some modifications I managed to got it working. This is the final code:

                        $pagina_id_test = get_the_id();
                        // retrieve all meta_values with key 'post_rating_0' from database
                        $reviews_posts  = $wpdb->get_results("
                            SELECT meta_value FROM " . $wpdb->prefix . "postmeta
                            WHERE meta_key = 'post_rating_0'
                            AND post_id = $pagina_id_test", ARRAY_A);
                        // define reviews array
                        $reviews_count  = array();

                        // iterate through meta_values, count the occurence of each review
                        foreach ($reviews_posts as $reviews_post) {
                            if (isset($reviews_count[$reviews_post['meta_value']])) {
                                $reviews_count[$reviews_post['meta_value']] = $reviews_count[$reviews_post['meta_value']] + 1;
                            } else {
                                $reviews_count[$reviews_post['meta_value']] = 1;
                            }
                        }
                        // echo results
                        $aantal_reviews = 0;
                        foreach ($reviews_count as $review) {
                            $aantal_reviews++;
                        }
                        echo $aantal_reviews;