Inpsyde\MultilingualPress\API\WPDBSiteRelations::get_related_site_ids PHP Method

    public function get_related_site_ids($site_id = 0, $include_site = false)
    {
        $site_id = $site_id ?: get_current_blog_id();
        if (!absint($site_id)) {
            return [];
        }
        $query = "\n(\n\tSELECT DISTINCT site_1 as site_id\n\tFROM {$this->table}\n\tWHERE site_2 = %d\n)\nUNION\n(\n\tSELECT DISTINCT site_2\n\tFROM {$this->table}\n\tWHERE site_1 = %d\n)\nORDER BY site_id ASC";
        $query = $this->db->prepare($query, $site_id, $site_id);
        $rows = $this->db->get_col($query);
        if (!$rows) {
            return [];
        }
        if ($include_site) {
            $rows[] = $site_id;
        }
        return array_map('intval', $rows);
    }