php – 不应该准备好更快的语句吗？

$s = explode (" ",microtime());
$s = $s[0]+$s[1];
$con = mysqli_connect ('localhost','test','pass','db') or die('Err');

for ($i=0; $i<1000; $i++) {

  $stmt = $con -> prepare( " SELECT MAX(id) AS max_id,MIN(id) AS min_id FROM tb ");
  $stmt -> execute();
  $stmt->bind_result($M,$m);
  $stmt->free_result();
  $rand = mt_rand( $m,$M ).'<br/>';

  $res = $con -> prepare( " SELECT * FROM tb WHERE id >= ? LIMIT 0,1 ");
  $res -> bind_param("s",$rand);
  $res -> execute();
  $res->free_result();
}

$e = explode (" ",microtime());
$e = $e[0]+$e[1];
echo  number_format($e-$s,4,'.','');

// and:

$link = mysql_connect ("localhost","test","pass") or die ();
mysql_select_db ("db") or die ("Unable to select database".mysql_error());

for ($i=0; $i<1000; $i++) {
  $range_result = mysql_query( " SELECT MAX(`id`) AS max_id,MIN(`id`) AS min_id FROM tb ");
  $range_row = mysql_fetch_object( $range_result ); 
  $random = mt_rand( $range_row->min_id,$range_row->max_id );
  $result = mysql_query( " SELECT * FROM tb WHERE id >= $random LIMIT 0,1 ");
}

准备好的陈述更加安全
但是每一个地方都说它们要快得多
但在我对上述代码的测试中,我有：
– 准备好的陈述2.45秒
– secon示例5.05秒

你觉得我做错了什么？
我应该使用第二种解决方案,还是应该尝试优化准备工作？