About the performance optimize question.(php or sql code)

As you know. In the query loop, the database query number will increase when every thumbnail shows.

For example the queries is 100+ if there are 100 posts in a page,like the code:

<?php
$args = array(
	'orderby' => 'rand',
	'posts_per_page' => 100,
);
$wp_query = new WP_Query($args);
while($wp_query->have_posts()):$wp_query->the_post();
	echo get_the_post_thumbnail();
endwhile;
echo '<br/>The queries is: ' . get_num_queries();
?>

Above code, you can get a large of database queries number(at least 100+). It is a big problem of performance. Do you think?

So, I figured out a idea to optimize it but i don’t know how to write the code. Please see my idea:
As you know, type print_r($post) , it will show the stdClass object of global $post in loop. Like this:

stdClass Object
(
    [ID] => 5915
    [post_author] => 1
    [post_date] => 2011-08-11 11:19:21
    [post_date_gmt] => 2011-08-11 03:19:21
    [post_content] => just_for_a_test_content
    [post_title] => just_for_a_test_title
    [post_excerpt] =>
    [post_status] => publish
    [comment_status] => open
    [ping_status] => open
    [post_password] =>
    [post_name] => just_for_a_test
    [to_ping] =>
    [pinged] =>
    [post_modified] => 2011-08-11 11:19:21
    [post_modified_gmt] => 2011-08-11 03:19:21
    [post_content_filtered] =>
    [post_parent] => 0
    [guid] => https://192.168.1.118/?p=5915
    [menu_order] => 0
    [post_type] => post
    [post_mime_type] =>
    [comment_count] => 18
    [filter] => raw
)

As you see, the stdClass object is not include [_wp_attached_file]. So I want to put the [_wp_attached_file] join into the stdClass. And after that I can use the code of $post->_wp_attached_file to show thumbnail url. But how to join and how to write the php or sql code?

I have a little idea. Maybe can use the code left join **** and add_filter('posts_join',***)….

Oh, please for help. Will you have a happy day ??