function get_post_meta_all($post_id){
    global $wpdb;
    $data   =   array();
    $wpdb->query("
        SELECT `meta_key`, `meta_value`
        FROM $wpdb->postmeta
        WHERE `post_id` = $post_id
    ");
    foreach($wpdb->last_result as $k => $v){
        $data[$v->meta_key] =   $v->meta_value;
    };
    return $data;
}

Gets all of a Wordpress post meta data in an array without specifying a key

Get all Wordpress post meta

wordpress

PHP