Mysql fetch array error

Im getting an error on my site that appeared for the first time today, despite functioning fine for months.

Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource in /web_directory/index.php on line 33

Here is the code from those lines.

<?  $sql = "SELECT 
            p.id as 'id',
            p.post_title as 'client',
            (SELECT `meta_value` FROM `wp_postmeta` WHERE `post_id` = p.id AND `meta_key` = 'thumb1') as 'thumb'
            FROM
            `wp_posts` p
            INNER JOIN `wp_postmeta` pm ON (p.id = pm.post_id)
            INNER JOIN `wp_term_relationships` wtr ON (p.id = wtr.object_id)
            INNER JOIN `wp_term_taxonomy` tt ON (wtr.term_taxonomy_id = tt.term_taxonomy_id)
            WHERE 
            tt.term_id = 439
            AND tt.taxonomy = 'category'
            AND p.post_status = 'publish'
            GROUP BY p.id
            ORDER BY p.id DESC
            LIMIT 5
            ";
    $sql = mysql_query($sql);
    $i=0;
    while($s = mysql_fetch_array($sql))
    {
        $i++;
?> 

Im not the original developer of the site, and I dont have much of a knowledge with mysql. Thanks 开发者_StackOverflow中文版for your awesome answers in advance!

There might be some error in your query; try adding or die(mysql_error()) to mysql_query like this:

$sql = mysql_query($sql) or die(mysql_error());

The mysql_query should return a resource identifier which you can check with:

if (!is_resource($sql)){
  die(mysql_error());
}

Obviously you are feeding mysql_fetch_array() not a valid MySQL result resource.

This might happen whenever mysql_query fails for any reason. (query is wrong, database has gone away, network is down, etc etc.)

You should check if a call to mysql_query is successfull before trying to iterate over its data. If you add a check and print out what the error really is, you might pin it down yourself.

For SELECT, SHOW, DESCRIBE, EXPLAIN and other statements returning resultset, mysql_query() returns a resource on success, or FALSE on error.

http://php.net/manual/en/function.mysql-query.php

Adding this before mysql_fetch_array() will make sure the script dies whenever an error has occurred including the actual error message:

$res = mysql_query($sql);
if (!$res) {
    die('Invalid query: ' . mysql_error());
}