public function getRelatedCompanies()
    {
        $conn = $this->app->getApplicationBox()->get_connection();

        $sql = 'SELECT DISTINCT Users.company ' . $this->generate_sql_constraints() . ' ORDER BY Users.company';

        $stmt = $conn->prepare($sql);
        $stmt->execute($this->sql_params);
        $rs = $stmt->fetchAll(PDO::FETCH_ASSOC);
        $stmt->closeCursor();

        $companies = [];
        foreach ($rs as $row) {
            if (trim($row['company']) === '') {
                continue;
            }
            $companies[] = $row['company'];
        }

        return $companies;
    }