<?php
declare(strict_types=1);

$db = new PDO("sqlite::memory:",null,null,[PDO::ATTR_ERRMODE=>PDO::ERRMODE_EXCEPTION]);
$db->exec("CREATE TABLE stock (id INTEGER PRIMARY KEY, available INTEGER NOT NULL CHECK(available >= 0))");
$db->exec("INSERT INTO stock VALUES (1,5)");
$reserve = $db->prepare("UPDATE stock SET available = available - :take WHERE id = :id AND available >= :needed");
foreach ([3,3] as $count) {
    $reserve->execute(["take"=>$count,"id"=>1,"needed"=>$count]);
    echo $reserve->rowCount() === 1 ? "Reserved\n" : "Insufficient stock\n";
}
echo $db->query("SELECT available FROM stock WHERE id=1")->fetchColumn(), " left\n";