pdo链接limit 后放变量出错，放数值能正常运行

 Fatal error: Call to a member function fetch() on a non-object

$page=$_GET['page'];

$sql='select * from demo1 limit' . $page . ',10';

$res=$pdo->query($sql);

while($row=$res->fetch(pdo::FETCH_ASSOC)){

print_r($row);

echo "<br>";

}