Why is error with activation of account?

[toplisek]

I have code when user clicks on link in his email and activates account.
error is:

Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource in activationuser.php on line 25 

Line 25 is: while ($row = mysql_fetch_array($result)) and all code:

$query = "SELECT * FROM membership WHERE activationnum = '$accountnum'";
  while ($row = mysql_fetch_array($result))
{           $activation = $row["activation"];
         if ($activation==1)

      {   echo "<script language='javascript'>
                    document.location='index.php';</script>";  }

       else
        {
            $query = "UPDATE membership SET activation ='1'
            WHERE activationnum = '$accountnum'";
            $result= mysql_query ($query) or die ('Can not complete update');

         }
 } 

I have to redirect user to index.php page if he clicks twice on link in his e-mail. So, only once can be pressed on link.

[bokeh]

Because you haven't run a query. You need the following on the second line of your post.

$result = mysql_query($query); 

[toplisek]

Thanks, it works now.