mysqli 的多sql语句执行有关问题

mysqli 的多sql语句执行问题

<?php<br />
	//对象创建<br />
	$mysqli = new mysqli('localhost', 'root', 'nagiosxi'，'hrsystem');<br />
	//连接是否出错<br />
	if($mysqli->connect_error)<br />
	{<br />
		die('connect database error'.mysqli_connect_error());<br />
	}<br />
	$sql = "insert into login (user, pass, email, type) values ('dengchao1', md5('dengchao123'), 'dengchao1@gmail.com', 0);";<br />
	$sql .= "insert into login (user1, pass, email, type) values ('dengchao1', md5('dengchao123'), 'dengchao1@gmail.com', 0)";<br />
	$res = $mysqli->multi_query($sql);<br />
	if($res && $mysqli->affected_rows > 0)<br />
	{<br />
		echo "insert ok <br />rows: ".$mysqli->affected_rows;<br />
	}<br />
	else<br />
	{<br />
		//$mysqli->close();<br />
		die('insert error <br />'.$mysqli->error.$mysqli->close());<br />
	}<br />
	if(!is_bool($res))<br />
	{<br />
		$res->free();<br />
	}<br />
<br />
	$sql = "select * from login";<br />
	$res = $mysqli->query($sql);<br />
        echo $mysqli->error."<br />";<br />
	if($res)<br />
	{<br />
		while($row = $res->fetch_row())<br />
		{<br />
			foreach($row as $key => $val)<br />
			{<br />
				echo "--$val";<br />
			}<br />
			echo "<br />";<br />
		}<br />
	}<br />
	if(!is_bool($res))<br />
	{<br />
		$res->free();<br />
	}<br />
	$mysqli->close();<br />
?>

为啥会报错：Commands out of sync; you can't run this command now
 这句报错，对应的查询语句是
$sql = "select * from login";
$res = $mysqli->query($sql);

非常不解，请答案，没百度到。
------解决方案--------------------
先把multi_query的结果集释放了,再进行查询