Wordpress query to show only sticky posts - php

Question

Following is my wordpress query in which i want to show only sticky posts but the query is not showing any posts. Also I set two posts as sticky so that part is checked!!!. Kindly let me know how to modify this query so it will only show the posts which are sticky
<?php
$wp_query = null;
$wp_query = new WP_Query(array(
'posts_per_page' => 2,
//'paged' => get_query_var('paged'),
'post_type' => 'post',
'post__in' => 'sticky_posts',
//'post__not_in' => array($lastpost),
'post_status' => 'publish',
'caller_get_posts'=> 0 ));
while ($wp_query->have_posts()) : $wp_query->the_post(); $lastpost[] = get_the_ID();
?>

Answer 1

Query which will show only sticky posts:
// get sticky posts from DB
$sticky = get_option('sticky_posts');
// check if there are any
if (!empty($sticky)) {
// optional: sort the newest IDs first
rsort($sticky);
// override the query
$args = array(
'post__in' => $sticky
);
query_posts($args);
// the loop
while (have_posts()) {
the_post();
// your code
}
}

Answer 2

The query_posts() function creates a new WP_Query() not before the current query is set up, meaning this is not the best efficient method and will perform extra SQL requests.
Use the 'pre_get_posts' hook to be safe, like
function sticky_home( $query ) {
$sticky = get_option('sticky_posts');
if (! empty($sticky)) {
if ( $query->is_home() && $query->is_main_query() ) {
$query->set( 'post__in', $sticky );
}
}
} add_action( 'pre_get_posts', 'sticky_home' );