latest-post-per-post-type-query.php

<?php
/*

  latest-post-per-post-type-query.php

  LatestPostPerPostTypeQuery class that extends WP_Query and provides the latest post for each post type passed

  Author: Mike Schinkel (http://mikeschinkel.com)

   Just drop this example into the root of your website and call directly to see it work.
   Use the class in your plugins or themes.

   In Answer To: http://wordpress.stackexchange.com/questions/2593/

   Reference: http://www.xaprb.com/blog/2006/12/07/how-to-select-the-firstleastmax-row-per-group-in-sql/

*/

include "wp-load.php";

class LatestPostPerPostTypeQuery extends WP_Query {
	var $flag;
	function __construct($args=array()) {
		$this->LatestPostPerPostTypeQuery($args);
	}
	function LatestPostPerPostTypeQuery($args=array()) {
		if (isset($args['post_type']) && !is_array($args['post_type']))
			$args['post_type'] = explode(',',$args['post_type']);
		$this->flag = true;
		parent::query($args);
	}
	static function on_load() {
		add_filter('posts_join',array(__CLASS__,'posts_join'),10,2);
	}
	static function posts_join($join,$query) {
		if (isset($query->flag)) {
			global $wpdb;
			$join .=<<<SQL
INNER JOIN (
SELECT post_type,MAX(post_date) AS post_date
FROM {$wpdb->posts}
GROUP BY post_type
ORDER BY COUNT(*) DESC
) max_date ON max_date.post_type={$wpdb->posts}.post_type AND max_date.post_date={$wpdb->posts}.post_date
SQL;
		}
		return $join;
	}
}
LatestPostPerPostTypeQuery::on_load();
?>
<ul>
<?php $query = new LatestPostPerPostTypeQuery(array('post_type'=>'eevents,winners,offers')); ?>
<?php while($query->have_posts()): $query->the_post(); ?>
	<li><?php the_title(); ?></li>
<?php endwhile; ?>
</ul>