Write SQL query to grab a custom field and insert it in the post meta title

See pertinent discussion in wp-hackers:
https://comox.textdrive.com/pipermail/wp-hackers/2009-January/023584.html

Thank you, this will get me somewhere!

I tried as written in the thread suggested and modified the plugin to include the SQL query

function sample_function() {
	global $post;
	$id = $post->ID;
	$town = get_post_meta($id, 'test', true);
	if ($town != '') {
	echo $town;}
	}

but it does not work at all.

This is the first plugin I am writing and I seem to be missing some vital part.

<?php
/*
Description: Posts the town to the meta title
 */
if (!class_exists("ThriftyPlugin")) {
	class ThriftyPlugin {
		function ThriftyPlugin() { //constructor

		}
		function addHeaderCode() {
			?>
<!-- Some test comment in the DOM -->
			<?php

		}
		function addContent($content = '') {
			$content .= "Some test content at end post
";
			return $content;
		}
		function authorUpperCase($author = '') {
			return strtoupper($author);
		}
      function sample_function() {
	global $post;
	$id = $post->ID;
	$town = get_post_meta($id, 'test', true);
	if ($town != '') {
	echo $town;}
	}

	}

} //End Class ThriftyPlugin

if (class_exists("ThriftyPlugin")) {
	$dl_PostToTitle = new ThriftyPlugin();
}
//Actions and Filters
if (isset($dl_PostToTitle)) {
	//Actions
	add_action('wp_head', array(&$dl_PostToTitle, 'addHeaderCode'), 1);
	//Filters
	add_filter('the_content', array(&$dl_PostToTitle, 'addContent'));
	add_filter('get_comment_author', array(&$dl_PostToTitle, 'authorUpperCase'));
}
?>

I have no idea how to hook the sample_function to make it work. I then need to make the content written within the <title></title> tags, but I’ll discover that later.
Any help on how to get the content echoed?

I am not going forward with this. I tried including the function with the following sql query:

function sample_function() {
		global $wpdb;
		$wpdb->query("
		UPDATE $wpdb->postmeta WHERE meta_key = 'test'");

But to no use. Also, what is the correct filter I should associate with this function? Any ideas anyone? HELP PLEASE!!

Ok I solved this the following way:

function post_the_meta() {
	global $wp_query;
	if ( is_single() ) {
		if ( $wp_query->post ) {
			$post = $wp_query->post;
			if ( get_post_meta( $post->ID, '$key', true ) ) {
				echo get_post_meta( $post->ID, '$key', true ) . "\n";
			}
		}
	}
}

Thanks to John Blackbourn and his Head Meta plugin