Get the comments of a post using SQL

Hello, how can I find and display the first comment of the current post I am reading?

I think a solution will be with SQL.

Any clues?
Thank you!

This is a function that gets 5 recent comments of all posts. I would like to edit this and show the latest of the post I am reading

function showLatestComments() {
      global $wpdb;
      $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'
       ORDER BY comment_date_gmt DESC
       LIMIT 5";
     $comments = $wpdb->get_results($sql);
     $output .= '<h2>latest comments</h2><ul id="comm">';
     foreach ($comments as $comment) {
       $output .= '<li><strong>'. $comment->comment_author . ' said</strong> : "' . strip_tags($comment->com_excerpt). '..."</li>';
       }
     $output .= '</ul>';
     echo $output;
    }//end function