How to get the most recent modified date of anything in the footer of my site?

Question

I would like to be able to post the most recent updated date in my footer. However, I can't seem to find a way to do that globally for the site, just for each post/page at a time using get_the_modified_date().

So for example if I make a change to my home page the footer would be updated to that date and time. If I later make an edit to a miscellaneous page, then the "Updated" date and time would change to reflect that more recent update.

Any help is greatly appreciated.

Answer 1

Just a continuation from mozboz' answer. For those curious as I was, you could use the date() or date_i18n() functions to format the date properly in the following snippet.

function get_latest_update_date() {
    global $wpdb;
    $thelatest = $wpdb->get_var("SELECT max(post_modified) FROM wp_posts WHERE post_type IN ('post', 'page');");
    //returns formatted date like 13.08.2001
    return date_i18n('j.m.Y', strtotime($thelatest));
  }
  
  add_shortcode('latestupdatedate', 'get_latest_update_date');

Answer 2

I don't know if there's a more WP-friendly way to do this, but this query will do what you want. It gets the latest date from the posts table for any post or page:

select max(post_modified) from wp_posts where post_type IN ('post', 'page');

So you could wrap that up in a shortcode for example, like:

function get_latest_update_date() {
  global $wpdb;
  return $wpdb->get_var("SELECT max(post_modified) FROM wp_posts WHERE post_type IN ('post', 'page');");
}

add_shortcode('latestupdatedate', 'get_latest_update_date');

If you want to format the date, you'll need to add the PHP date parsing/formatting functions.