Missing Argument 2 For WPDB

I am trying to run the below query and output but getting the error as seen below. I get you should add an argument but with a query that really doesnt have one what do you do?

Just trying to get all email addresses from comments and display them.

$myrows = $wpdb->get_results( $wpdb->prepare("SELECT DISTINCT comment_author_email FROM wp_comments" ));
foreach ( $myrows as $myrows )
{
	echo $myrows->comment_author_email;
}

Warning: Missing argument 2 for wpdb::prepare()

Thanks!