Prepared statement vs transaction in PDO

[beipink]

qual'è la vera differenza tra Prepared statement

<?php
/* Execute a prepared statement by binding PHP variables */
$calories = 150;
$colour = 'red';
$sth = $dbh->prepare('SELECT name, colour, calories
    FROM fruit
    WHERE calories < :calories AND colour = :colour');
$sth->bindParam(':calories', $calories, PDO::PARAM_INT);
$sth->bindParam(':colour', $colour, PDO::PARAM_STR, 12);
$sth->execute();
?>

e una cosa tipo questa?

<?php
/* Begin a transaction, turning off autocommit */
$dbh->beginTransaction();
/* Change the database schema and data */
$sth = $dbh->exec("DROP TABLE fruit");
$sth = $dbh->exec("UPDATE dessert
    SET name = 'hamburger'");
$dbh->Commit();
/* Recognize mistake and roll back changes */
$dbh->rollBack();
/* Database connection is now back in autocommit mode */
?>

Qual'è + indicato usare per una programmazione corretta. Per esempio: nel libro "Beginning PHP and PostgreSQL E-Commerce from novice to professional" non usano $dbh->beginTransaction(); usano prepare() e execute() ma non usano bindParam().

grazie