Get Comments From Post ID -- SQL method help!

CMS & WordPress
1

I’ll split my question in two parts: First; Am I going about this the right way and Second; See the SQL string below (Any feedback is welcome)

Basically, I have a plugin that pulls content from a post based on a slug wrapped in [[post-title]]. You can then go to a page, insert this shortcode-hybrid syntax directly into the text field, and the page will spit out the content from the selected post ID.

I need to attach the comments from that post to the bottom of the content. I figure there’s two ways to attack the problem:

A) use the template_tags
use the $wpdb

I’m using the latter method and I try placing a variable in the SQL string:

WHERE comment_approved = ‘1’ AND comment_post_id='" . $post_id . '"

Unfortunately this does not work.

I have a plugin that I’m trying to add a script that pulls comments based on a post_id

I read somewhere that this script would work but it does not:

$sql = "
	   SELECT DISTINCT comment_post_ID, comment_author, comment_date_gmt, comment_approved, SUBSTRING(comment_content,1,100) AS com_excerpt 
	   FROM $wpdb->comments 
	   WHERE comment_approved = '1' AND comment_post_id = %s
	   ORDER BY comment_date_gmt DESC 
	   LIMIT 5", ($post);

I get a fatal error: unexpected ‘,’ on that last line…
$post is defined in another function (in my plugin):

$post = $wpdb->get_var( $wpdb->prepare( "SELECT ID FROM $wpdb->posts WHERE post_name = %s", $post_name ));
	if ( $post ) return get_post($post, $output);
	return null;
	}

Thanks for your help!
Alex