$sql = $DBH->prepare("INSERT INTO $students (name, secname, sex, group, email, mark, year, city) values (:name, :secname, :sex, :group, :email, :mark, :year, :city)");
$sql->execute((array)$student);

//eror:
Uncaught exception 'PDOException' with message 'SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '(name, secname, sex, group, email, mark, year, city)