function shortcode to create plugin : latest comments meta_value

Hi everybody
I’m looking for help to create a shortcode which calls specific field from commentmeta – meta_value.

Here is the sql query :

<? $select = "SELECT meta_value FROM " . "$wpdb->commentmeta WHERE meta_key='pmg_comment_title' AND meta_value!=''";
		$requete = $wpdb->get_results($select);
		foreach($requete as $ligne){?>

		<?php echo $ligne->meta_value; echo'<br/>';
		}
		?>

The begining of the fucntion should be ?

function MYshorcode_shortcode( $atts )
{
/// I don't know how to call sql
add_shortcode('MYshortcode', 'MYshortcode_shortcode');

I’m newbie in WP hack, so I don’t understand how to create a function then a shortcode to make the query works in a widget.

I’ve also add to my function.php file :
add_filter('widget_text', 'do_shortcode');

Thank’s for your help !

(excuse my bad english ;))