$db = Db::getConnection();
$sql = 'INSERT INTO table VALUES (NULL, :a, :b)';
$result = $db->prepare($sql);
$result->bindParam(':a', $a, PDO::PARAM_INT);
$result->bindParam(':b', $b, PDO::PARAM_INT);
$result->execute();
$increment = Functions::get_increment($a, $b);