Ordering Wordpress posts by most recent comment

Assign

select wp_posts.*, max(comment_date) as max_comment_date
from $wpdb->posts wp_posts
right join $wpdb->comments
on id = comment_post_id
group by ID
order by max_comment_date desc
limit 10

to some variable $query. You can fiddle around with the 10 or the query itself. (I'm no SQL optimization ninja.) Then your code will look something like

<?php
     $results = $wpdb->get_results($query) or die('!');
     foreach ($results as $result):
?>
[insert template here]
<?php endforeach ?>

This pattern is covered in more depth by the Codex.

OK guys,

A lot of great answers here, but obviously nobody's taken the time to test them.

Hao Lian gets the credit for the first best original answer, but unfortunately his code doesn't show posts without comments.

Captain Keytar is on the right track, but his code will display every single post and attachment as a separate result.

Here is a modified version of Captain Keytar but it limits the results to the type 'post'.. that has been published (to avoid getting drafts!!)

    select wp_posts.*,
    coalesce(
        (
            select max(comment_date)
            from $wpdb->comments wpc
            where wpc.comment_post_id = wp_posts.id
        ),
        wp_posts.post_date
    ) as mcomment_date
    from $wpdb->posts wp_posts
    where post_type = 'post'
    and post_status = 'publish' 
    order by mcomment_date desc
    limit 10

I used a simpler, portion of a native WP in function. hope it helps and some one can continue to develop. Here is a simplified version that shows the title & excerpt of the post along with the comment content & author from the latest commented posts using get_comments.

    $args = array(
        'status' => 'approve',
        'number' => 6,
        'order' => 'DESC'
    );
    $comments = get_comments($args);

    foreach($comments as $comment) : $count++;

            $post_args = array(
                'post_type' => 'post',
                'p' => $comment->comment_post_ID,
                'posts_per_page' => 1
                );

            $posts = get_posts($post_args);

            foreach($posts as $post) : setup_postdata($post);

                the_title();
                the_excerpt();

            endforeach;

        echo $comment->comment_content;     
        echo $comment->comment_author;

    endforeach;