mysql_fetch_array(): supplied argument is not a valid yardım

 <?php 
include("baglan.php"); 

$id=$_GET["id"]; 

$katcek=mysql_query("select * from kategoriler where katid='$id'"); 
while($yaz=mysql_fetch_array($katcek)){ 
$id=$yaz['id']; 
$baslik=$yaz['baslik']; 

echo $baslik;
}
  



?>

echo mysql_num_rows($katcek);
exit;