Function to automatically plug the date of first post into footer for copyright purposes.

first_date_footer.php

/**
 * This is a function to automatically plug the date of first post into footer.
 * 
 * @package CWS Core Functionality
 * @since   1.0.0
 * @author  Cap Web Solutions
 * @license GPL-2.0+
 * 
 * @return void
 */
function cws_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;
}