Here’s another little function that tends to come in handy. Recently, on a project I did for a client, they had a sidebar where they wanted to display pages that were children of a main page. I whipped up this function to get the ID of a page’s slug and then perform a query:

function get_ID_by_slug($page_slug) {
    $page = get_page_by_path($page_slug);
    if ($page) {
        return $page->ID;
    } else {
        return null;

So for example, you could then do a query like this in your sidebar:

$querystr = "SELECT wposts.* FROM $wpdb->posts wposts WHERE wposts.post_parent = '".get_ID_by_slug("white-papers")."' AND wposts.post_status = 'publish' AND wposts.post_type = 'page'";

And you would get all pages that are children of “white-papers”, it’s basic I know, but it works, and has a few other uses than just where I used it.