php 判断查询结果是否为空

select count(people) c from people where people='乐乐'

<?php
$p=$_POST['p'];
$cnx = new PDO("odbc:Driver={SQL Server};Server=;Database=;",'','');
$ps=$cnx->query("select count(people) c from people where people='".$p."'");
foreach($ps as $s){
if ($s['c']=='0'){
echo "用户可用";
}else{
echo "此用户名已存在";
}

}
?>