Output copyright with creation date

<?php 
function yoolk_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 = "&copy; " . $copyright_dates[0]->firstdate;
		if($copyright_dates[0]->firstdate != $copyright_dates[0]->lastdate) {
			$copyright .= '-' . $copyright_dates[0]->lastdate;
		}
		$output = $copyright.' - Website made by Yoolk';
	}
	return $output;
} ?>