If you need to debug what queries your WordPress site is making, try adding the following PHP to your theme:

<?php
  foreach ( $wpdb->queries as $query ) {
    echo "$query[0]<br />";
  }
?>

For this code to work, you need to add the following line to wp-config.php:

define('SAVEQUERIES', true);

After that, you should see a list of queries that was used to generate the latest page view.