如何设置value=$sum的最大值

我有一个选项让用户给其他用户点

我想确保他们给的分数不会超过他们的分数。

我该怎么做?

maxvalue无效

<?php
$user=$_SESSION['SESS_USERID'];
if(isset($_REQUEST['user'])){
$user = preg_replace('#[^a-z0-9]#i', '', $_GET['user']);
}
$sql=mysqli_query($conn,"SELECT SUM(sterren) AS total FROM sterren WHERE userid='$user'");
if ($row = mysqli_fetch_assoc ($sql)){
$sum = $row['total'];
if ($row["total"] >= '1') {
echo"
<table>
<some form action>
///Some more code to select the user to give the points to
<input type='text' name='sterren' id='sterren' size='3' maxlength='3' maxvalue=$sum ></td>
</form>
</table>";
}
}
<?