what happens if antoher transaction is started php code example

Example 1: php pdo transaction

$pdo = new PDO(
    $dsn, 
    $username, 
    $password, 
    array(PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION)
);

try {
    $statement = $pdo->prepare("UPDATE user SET name = :name");

    $pdo->beginTransaction();

    $statement->execute(["name"=>'Bob']);
    $statement->execute(["name"=>'Joe']);

    $pdo->commit();
} 
catch (\Exception $e) {
    if ($pdo->inTransaction()) {
        $pdo->rollback();
        // If we got here our two data updates are not in the database
    }
    throw $e;
}

Example 2: php pdo transaction

// In this example we are using MySQL but this applies to any database that has support for transactions
$db = new PDO('mysql:host=' . $host . ';dbname=' . $dbname . ';charset=utf8', $username, $password);    

// Make sure that PDO will throw an exception in case of error to make error handling easier
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

try {
    // From this point and until the transaction is being committed every change to the database can be reverted
    $db->beginTransaction();    
    
    // Insert the metadata of the order into the database
    $preparedStatement = $db->prepare(
        'INSERT INTO `orders` (`order_id`, `name`, `address`, `created_at`)
         VALUES (:name, :address, :telephone, :created_at)'
    );
    
    $preparedStatement->execute([
        'name' => $name,
        'address' => $address,
        'telephone' => $telephone,
        'created_at' => time(),
    ]);
    
    // Get the generated `order_id`
    $orderId = $db->lastInsertId();

    // Construct the query for inserting the products of the order
    $insertProductsQuery = 'INSERT INTO `orders_products` (`order_id`, `product_id`, `quantity`) VALUES';
    
    $count = 0;
    foreach ( $products as $productId => $quantity ) {
        $insertProductsQuery .= ' (:order_id' . $count . ', :product_id' . $count . ', :quantity' . $count . ')';
        
        $insertProductsParams['order_id' . $count] = $orderId;
        $insertProductsParams['product_id' . $count] = $productId;
        $insertProductsParams['quantity' . $count] = $quantity;
        
        ++$count;
    }
    
    // Insert the products included in the order into the database
    $preparedStatement = $db->prepare($insertProductsQuery);
    $preparedStatement->execute($insertProductsParams);
    
    // Make the changes to the database permanent
    $db->commit();
}
catch ( PDOException $e ) { 
    // Failed to insert the order into the database so we rollback any changes
    $db->rollback();
    throw $e;
}