How do I create a dynamically-updated copyright statement?

Question

I'd like to find an optimized, WP_Query-safe method for generating a dynamically-populated copyright statement for the bottom of my themes. That is to say, I'd like to check the date (by year) of my oldest and newest posts and then output something along the lines of

[blog name] © [oldest post year]-[newest post year] [primary blog author]

What's the easiest/safest way to do so?

Answer 1

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?