为什么空提交内容后显示这个？

<code>


      <meta charset="utf-8">
    <title></title>


<form method="post">
    <input type="text" name="num">
    <button type="submit">提交</button>
</form>
<?php if (isset($_POST['num'])) {
$pdo=new PDO("mysql:host=localhost;dbname=t1","root","");
$stmt=$pdo->prepare("select * from aaa where num=?");
$stmt->execute(array($_POST['num']));
$res=$stmt->fetchall(PDO::FETCH_ASSOC);
if($res){   
         foreach($res as $v){
          echo $v['name'];
         }
       }else{
        echo "没有";
       }
}else{
    echo "你还没有输入";
}
?>


</code>

<code>


      <meta charset="utf-8">
    <title></title>


<form method="post">
    <input type="text" name="num">
    <button type="submit">提交</button>
</form>
<?php if (isset($_POST['num'])) {
$pdo=new PDO("mysql:host=localhost;dbname=t1","root","");
$stmt=$pdo->prepare("select * from aaa where num=?");
$stmt->execute(array($_POST['num']));
$res=$stmt->fetchall(PDO::FETCH_ASSOC);
if($res){   
         foreach($res as $v){
          echo $v['name'];
         }
       }else{
        echo "没有";
       }
}else{
    echo "你还没有输入";
}
?>


</code>