PHP5 PDO 取得結果的數量或是陣列數量

<?php
 header("Content-Type:text/html; charset=utf-8");

 $db = new PDO('mysql:host=IP;dbname=test', '帳號', '密碼',
 array(PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES 'utf8';"));
 $db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

 try{

  $sql = "SELECT * FROM `...`";
  $data = $db->query($sql);

  //一次性讀取
  $rows = $data->fetchAll(PDO::FETCH_ASSOC);

  //取得數量
  echo "Row count:" .$data->rowCount() . "<br>";

  //取得陣列數量
  echo "Array count:" . count($rows) . "<br>";

  foreach ($rows as $key => $value) {
   var_dump($value);
   echo "<br>";
  }

 }catch(PDOException $ex){
  echo $ex;
 }
?>

參考資料：
http://www.php.net/manual/en/pdostatement.rowcount.php
http://tw2.php.net/count