[opgelost]sql query

<?php
$res = mysql_query("SELECT id FROM categorie ORDER BY id");
while ($arr = mysql_fetch_row($res))
{
    for ($i = 0; $i <= count($arr)-1; $i++)
    {
        $red = mysql_query("SELECT naam FROM categorie WHERE id=".$arr[$i]."");
        while ($obj = mysql_fetch_object($red))
        {
            echo $obj->naam.'<br />';
        }

        $red = mysql_query("SELECT * FROM product WHERE catid=".$arr[$i]." ORDER BY artnr");
        while ($obj = mysql_fetch_object($red))
        {
            echo $obj->artnr.' - '.$obj->productnaam;
        }
    }
}
?>

<?php
$res = mysql_query("SELECT id FROM categorie ORDER BY id");
while ($arr = mysql_fetch_row($res))
{
    for ($i = 0; $i <= count($arr)-1; $i++)
    {
        $red = mysql_query("SELECT naam FROM categorie WHERE id=".$arr[$i]."");
        while ($obj = mysql_fetch_object($red))
        {
            echo $obj->naam.'<br />';
        }
 
        $red = mysql_query("SELECT * FROM product WHERE catid=".$arr[$i]." ORDER BY artnr");
        while ($obj = mysql_fetch_object($red))
        {
            echo $obj->artnr.' - '.$obj->productnaam;
        }
    }
}
?>

ORDER BY id

ORDER BY id

ORDER BY id ASC

ORDER BY id ASC

ORDER BY id

ORDER BY id

ORDER BY id DESC

ORDER BY id DESC

<?php
$res = mysql_query("SELECT c.naam AS catnaam, p.artnr, p.productnaam FROM categorie c, product p WHERE c.id = p.catid ORDER BY c.id ASC, p.id ASC");
$cat = "";
while ($row = mysql_fetch_array($res, MYSQL_ASSOC))
{
  if($cat != $row[catnaam])
  {
    echo htmlentities($row[catnaam]) . "<br />";
    $cat = $row[catnaam];
  }

  echo $row[artnr] . " - " . $row[productnaam];
}
?>

<?php
$res = mysql_query("SELECT c.naam AS catnaam, p.artnr, p.productnaam FROM categorie c, product p WHERE c.id = p.catid ORDER BY c.id ASC, p.id ASC");
$cat = "";
while ($row = mysql_fetch_array($res, MYSQL_ASSOC))
{
  if($cat != $row[catnaam])
  {
    echo htmlentities($row[catnaam]) . "<br />";
    $cat = $row[catnaam];
  }
 
  echo $row[artnr] . " - " . $row[productnaam];
}
?>

Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource in C:\wamp\www\inc\test.php on line 6

Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource in C:\wamp\www\inc\test.php on line 6

<?php
while ($row = mysql_fetch_array($res, MYSQL_ASSOC))
?>

<?php
while ($row = mysql_fetch_array($res, MYSQL_ASSOC))
?>