foreach循环吃数据

Question

我有以下代码和输出。在循环注释＃2被注释＃1的数据覆盖后，这怎么可能？

<?php
    echo "<pre>".print_r($notes, true)."</pre>";

    foreach($notes as $k=>$note){
        // nothing here
    }

    echo "<pre>".print_r($notes, true)."</pre>";
?>

输出结果为：

Array
(
    [3] => Array
        (
            [created] => 2015-11-17 13:22:19
            [user] => 249340
            [text] => test
            [important] =>
            [author] => Joe
        )

    [2] => Array
        (
            [created] => 2015-11-17 12:52:44
            [user] => 249340
            [text] => He is Spanish
            [important] =>
            [author] => Bill
        )

    [1] => Array
        (
            [created] => 2015-11-17 12:52:28
            [user] => 249340
            [text] => He is a clown
            [important] => 1
            [firstname] => Bill
        )

)

Array
(
    [3] => Array
        (
            [created] => 2015-11-17 13:22:19
            [user] => 249340
            [text] => test
            [important] =>
            [author] => Joe
        )

    [2] => Array
        (
            [created] => 2015-11-17 12:52:28
            [user] => 249340
            [text] => He is a clown
            [important] => 1
            [firstname] => Bill
        )

    [1] => Array
        (
            [created] => 2015-11-17 12:52:28
            [user] => 249340
            [text] => He is a clown
            [important] => 1
            [author] => Bill
        )

)

定义$notes的代码：

<?php 
    $query = "SELECT * FROM notes WHERE user=249340";
    $select = $mysqli->query($query);

    while ($row = $select->fetch_assoc()) {
        $notes[$row['id']] = array_filter($row,function($var){return
!is_null($var);});
        unset($notes[$row['id']]["id"]);
    }
    $select->free();

    if(!count($notes)) {
        $notes = NULL;
    }

    krsort($notes);
?>