Dynamic Copyright Date

if ( ! function_exists( 'wpb_copyright' ) ) {

    function wpb_copyright() {

        // Cache the output so we don't have to run the query on every page load.

        $output = get_transient( 'wpb_copyright_text' );

        if ( false !== $output ) {

            // Return the cached output.

            return $output;

        }

        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 ) {

            $output = '© ' . $copyright_dates[0]->firstdate;

            if ( $copyright_dates[0]->firstdate !== $copyright_dates[0]->lastdate ) {

                $output .= '-' . $copyright_dates[0]->lastdate;

            }

            // Set the value as a transient so we only run the query 1x per day.

            set_transient( 'wpb_copyright_text', $output, DAY_IN_SECONDS );

        }

        return $output;

    }

}

echo wpb_copyright();