get_pending_comments_num( int|array $post_id )

function get_pending_comments_num( $post_id ) {
	global $wpdb;

	$single = false;
	if ( !is_array($post_id) ) {
		$post_id_array = (array) $post_id;
		$single = true;
	} else {
		$post_id_array = $post_id;
	}
	$post_id_array = array_map('intval', $post_id_array);
	$post_id_in = "'" . implode("', '", $post_id_array) . "'";

	$pending = $wpdb->get_results( "SELECT comment_post_ID, COUNT(comment_ID) as num_comments FROM $wpdb->comments WHERE comment_post_ID IN ( $post_id_in ) AND comment_approved = '0' GROUP BY comment_post_ID", ARRAY_A );

	if ( $single ) {
		if ( empty($pending) )
			return 0;
		else
			return absint($pending[0]['num_comments']);
	}

	$pending_keyed = array();

	// Default to zero pending for all posts in request
	foreach ( $post_id_array as $id )
		$pending_keyed[$id] = 0;

	if ( !empty($pending) )
		foreach ( $pending as $pend )
			$pending_keyed[$pend['comment_post_ID']] = absint($pend['num_comments']);

	return $pending_keyed;
}