mysqli查詢資料始終為null解決辦法

mysqli查詢資料始終為null
代碼如下，測試好多遍，始終不知道原因，Sql語句在Navicat裡邊有查詢結果，大家幫我看看：
function db_connect(){
$db=new mysqli("127.0.0.1", "root","admin159753","51dm","utf8");
$db->set_charset('utf8');
if (!$db) {
echo "Cloud not connect to database";
} else {
return $db;
}
}

$DB=db_connect();
$type="首頁駐站作品";
$query = "select * from picture where type='首頁駐站作品' order by chage_date desc";
$rs = $DB->query($query);

if (mysqli_num_rows($rs)==0) {
echo "num rows: 0";
}

if ($rs) {
echo "rs";
} else {
echo "查詢失敗";
}
?>
------解決思路----------------------
$query = "select * from picture where type='首頁駐站作品' order by chage_date desc";
如果是同樣的查詢語句，很有可能是字元集的原因。
你php的檔案編碼是utf-8的麼
------解決思路----------------------
$db=new mysqli("127.0.0.1", "root","admin159753","51dm","utf8");

$query = "select * from picture where type='首頁駐站作品' order by chage_date desc";
$rs = $DB->query($query);
------解決思路----------------------

