Selecting posts that match 2 categories

Hi everyone,

I’m trying to select posts that match 2 categories using a SELECT query. I know I’m close but right now it’s returning posts that have one or the other value while I only want it to return posts that match BOTH values.

Here’s the code…

<?php
global $wpdb;
global $post;

global $cseries;

$cquery = "SELECT option_value FROM $wpdb->options WHERE option_id=521";
$cseries = $wpdb->get_var($cquery);

 $querystr = "
    SELECT wposts.*
    FROM $wpdb->posts wposts
		INNER JOIN $wpdb->postmeta wpostmeta ON wposts.ID = wpostmeta.post_id
		INNER JOIN $wpdb->term_relationships ON (wposts.ID = $wpdb->term_relationships.object_id)

    WHERE wpostmeta.post_id = $wpdb->term_relationships.object_id
	AND wpostmeta.meta_key = '_edit_last'
	AND $wpdb->term_relationships.term_taxonomy_id = $cseries OR $wpdb->term_relationships.term_taxonomy_id = '4'
 ";

 $pageposts = $wpdb->get_results($querystr, OBJECT);
 echo $pageposts.term_taxonomy_id;
 ?>
<?php if ($pageposts): ?>
	<?php foreach ($pageposts as $post): ?>
	  <li><a href="<?php the_permalink() ?>" rel="bookmark"><?php the_title(); ?></a></li>
	<?php endforeach; ?>
<?php endif; ?>

Can anyone help? Thanks in advance!