How do I create a dynamically-updated copyright statement?

Here’s what I use:

function oenology_copyright() {
    global $wpdb;
    $copyright_dates = $wpdb->get_results("
        SELECT
            YEAR(min(post_date_gmt)) AS firstdate,
            YEAR(max(post_date_gmt)) AS lastdate
        FROM
            $wpdb->posts
        WHERE
            post_status="publish"
    ");
    $output="";
    if($copyright_dates) {
        $copyright = "© " . $copyright_dates[0]->firstdate;
            if($copyright_dates[0]->firstdate != $copyright_dates[0]->lastdate) {
                $copyright .= '-' . $copyright_dates[0]->lastdate;
            }
        $output = $copyright;
    }
    return $output;
}

Of course, if there’s a cleaner, safer, or more efficient method, I’d love to hear about it, too!

EDIT:

And here’s a more cleaned-up version, that adds the copyright dates to wp_cache:

function oenology_copyright() {
    // check for cached values for copyright dates
    $copyright_cache = wp_cache_get( 'copyright_dates', 'oenology' );
    // query the database for first/last copyright dates, if no cache exists
    if ( false === $copyright_cache ) { 
        global $wpdb;
        $copyright_dates = $wpdb->get_results("
            SELECT
            YEAR(min(post_date_gmt)) AS firstdate,
            YEAR(max(post_date_gmt)) AS lastdate
            FROM
            $wpdb->posts
            WHERE
            post_status="publish"
        ");
        $copyright_cache = $copyright_dates;
        // add the first/last copyright dates to the cache
        wp_cache_set( 'copyright_dates', $copyright_cache, 'oenology', '604800' );
    }
    // Build the copyright notice, based on cached date values
    $output="© ";
    if( $copyright_cache ) {
        $copyright = $copyright_cache[0]->firstdate;
        if( $copyright_cache[0]->firstdate != $copyright_cache[0]->lastdate ) {
            $copyright .= '-' . $copyright_cache[0]->lastdate;
        }
        $output .= $copyright;
    } else {
        $output .= date( 'Y' );
    }
    return $output;
}

Would this improve performance a bit?