Page Excerpt Outside the Loop

I need to show various excerpt from specific pages..

I found this code:

function get_the_excerpt_here($post_id)
{
  global $wpdb;
  $query = "SELECT post_excerpt FROM $wpdb->posts WHERE ID = $post_id LIMIT 1";
  $result = $wpdb->get_results($query, ARRAY_A);
  return $result[0]['post_excerpt'];
}

But I’m not sure how to use it.. I tried
<?php echo get_the_excerpt_here(12); ?>

but it doesn’t work..