I'm writing a script to display the 10 most recently "active" WordPress blog posts (i.e. those with the most recent comments). Problem is, the list has a lot of duplicates. I'd like to weed out the duplicates. Is there an easy way to do this by changing the MySQL query (like IGNORE, WHERE) or some other means? Here's what I have so far:

<?php

function cd_recently_active() {
    global $wpdb, $comments, $comment;
    $number = 10; //how many recently active posts to display? enter here

if ( !$comments = wp_cache_get( 'recent_comments', 'widget' ) ) {
    $comments = $wpdb->get_results("SELECT comment_date, comment_author, comment_author_url, comment_ID, comment_post_ID, comment_content FROM $wpdb->comments WHERE comment_approved = '1' ORDER BY comment_date_gmt DESC LIMIT $number");

    wp_cache_add( 'recent_comments', $comments, 'widget' );
}
?>