checkbox code php

////Code for obtaining and displaying Checkbox list
<div id="exxx">
<fieldset><legend>Select Export Fields</legend>
<?php
$result=mysql_query("desc student_test",$conn);
echo '<ul id="unshund">';
while($row=mysql_fetch_array($result))
{
$val=$row['Field'];
?>
<script language="JavaScript">
$(function(){
$("#chkAll").change(function(){
if (this.checked == true) {
$("input:checkbox.child").attr("checked", "checked");
}
else {
$("input:checkbox.child").removeAttr("checked");
}
});
});
</script>

<li ><input type='checkbox' class="child" name='' id=<?php echo $val; ?> value=<?php echo $val; ?> onchange="javascript:selectedField(this.id)" <?php if(isset($_SESSION['selectedFields'][$val])) { echo 'checked="checked"';} ?> /> <?php echo ucfirst($row['Field']);?> </li>
<?php
}
echo '</ul>';
?>
<input type="checkbox" id="chkAll" /> Toggle All<br/>