Warning:mysql_num_rows():suppliedargumentisnotavalidMySQLresultresourc,该如何解决

Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resourc

include("conn.php");
$SQL="SELECT * FROM `liuyanban` order by id desc";
$query=mysql_query($SQL);


$total=mysql_num_rows($query);
$pagesize=3;
$end_page=ceil($total/$pagesize);
$page = $_GET['page']; //当前页
if($page<=0)
{
$page =1;
}

if($page>$end_page)
{
$page=$end_page;
}
$start = ($page- 1)*$pagesize;
$sql = "select * from liuyanban limit $start, $pagesize ";

//mysql_query("set names 'GBK'");
$ros = mysql_query($sql,$connect);
?>


echo "留言表";
echo "
";
echo "当前第[$page]页,共[$end_page]页";
if($page==1)
{

?>
首页
}else
{
?>
首页


}
?>

" >上一页
" >下一页

if($page==$end_page)
{
?>
尾页
}else
{
?>
">尾页
}
?>

while ($row=mysql_fetch_array($ros)){
?>






}
?>

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------解决方案--------------------
$query=mysql_query($SQL) or die(mysql_error());