mysqli 的多sql語句執行有關問題

mysqli 的多sql語句執行問題

//對象建立
$mysqli = new mysqli('localhost', 'root', 'nagiosxi'，'hrsystem');
//串連是否出錯
if($mysqli->connect_error)
{
die('connect database error'.mysqli_connect_error());
}
$sql = "insert into login (user, pass, email, type) values ('dengchao1', md5('dengchao123'), [email protected]', 0);";
$sql .= "insert into login (user1, pass, email, type) values ('dengchao1', md5('dengchao123'), [email protected]', 0)";
$res = $mysqli->multi_query($sql);
if($res && $mysqli->affected_rows > 0)
{
echo "insert ok 
rows: ".$mysqli->affected_rows;
}
else
{
//$mysqli->close();
die('insert error 
'.$mysqli->error.$mysqli->close());
}
if(!is_bool($res))
{
$res->free();
}

$sql = "select * from login";
$res = $mysqli->query($sql);
        echo $mysqli->error."
";
if($res)
{
while($row = $res->fetch_row())
{
foreach($row as $key => $val)
{
echo "--$val";
}
echo "
";
}
}
if(!is_bool($res))
{
$res->free();
}
$mysqli->close();
?>

為啥會報錯：Commands out of sync; you can't run this command now
這句報錯，對應的查詢語句是
$sql = "select * from login";
$res = $mysqli->query($sql);

非常不解，請答案，沒百度到。
------解決方案--------------------
先把multi_query的結果集釋放了,再進行查詢

