inner join

[seokey]

Salve a tutti,

cosa sto sbagliando in questa inner join?

  <?php include("articolipselect.php"); ?></span></td>
      <form action="articoli.php" method="post" enctype="multipart/form-data" name="form1"><td bgcolor="#999999">
       <input name="posted" type="hidden" id="posted2" value="posted2" />
      <?php 
  include ("config.inc.php"); 
  include ("connect.php");
    $idcat = $_POST['idcat'];
    echo $idcat;
    if(isset($_POST['posted'])) {
  $query ="SELECT * FROM democat AS c, demosubcat AS s WHERE c.idcat=s.idcat AND idcat='$idcat'";
  $result = mysql_query($query,$db);
     echo  "<select name=\"subcategoria\">";
  while ($row = mysql_fetch_array($result)) {
  echo "<option value=\"".$row['subcategoria']."\">".$row['subcategoria']."</option>";}
  echo"</select>"; } ?></td>

Recupero il valore $idcat da categoria e voglio verificarlo con $idcat presente su sottocategorie...