$sql = 'SELECT name,colour,calories FROM fruit WHERE calories < :calories AND colour = :colour';
$sth = $dbh->prepare($sql,array(PDO::ATTR_CURSOR => PDO::CURSOR_FWDONLY));
$sth->execute(array(':calories' => 150,':colour' => 'red'));
$red = $sth->fetchAll();

VS

$sql = "SELECT name,calories FROM fruit WHERE calories < $calories AND colour = $colour";
$result = $connection->query($query);
$row = $result->fetch(PDO::FETCH_ASSOC);

两个查询都将返回相同的结果,所以为什么使用准备,对我来说看起来它会慢,因为你必须执行额外的步骤.

谢谢