dedecms怎么判断二级栏目为空不显示

{dede:channelartlist typeid='top'}
<li><a href="{dede:field name=&#39;typeurl&#39;/}">{dede:field name=&#39;typename&#39;/}</a>
{dede:php}
$id = $refObj->Fields[&#39;id&#39;];
$sql = ("SELECT * FROM dede_arctype where reid =&#39;$id&#39;");
$db->SetQuery($sql);
$db->Execute();
if($db->GetTotalRow()){
echo &#39;<ul>&#39;;
while($row = $db->GetArray()){
$url = str_replace(&#39;{cmspath}&#39;,&#39;&#39;,($row[typedir]));
echo "<li><a href=".$url.">".($row[typename])."</a></li>";
};
echo &#39;</ul>&#39;;
};
{/dede:php}
</li>
{/dede:channelartlist}