DELETE FROM comment
WHERE nid = <the involved node id>

SELECT * FROM comment
WHERE nid = <the involved node id>

DELETE FROM field_data_comment_body
WHERE entity_type = "comment"
AND entity_id IN (
  SELECT cid
  FROM comment
  WHERE nid = <the involved node id>
)

<?php

// Change this to the nid you want to clear comments from
$nid = 12345;

// Queries the database for all comment IDs associated with the nid, max 1000
$cids = db_select('comment', 'c')
  ->fields('c', array('cid'))
  ->condition('c.nid', $nid)
  ->range(0, 1000)
  ->execute()
  ->fetchCol();

if (!count($cids)) {
  drush_print("No more comments found. Aborting.");

  // Abort with an error code (so a bash script can key off that)
  exit(1);
}

// Delete the comments with comment IDs we got from the DB
comment_delete_multiple($cids);
drush_print(count($cids) . " comments deleted");

#!/bin/bash

while drush @your-server-alias scr /path/to/script/on/server/so.php; do
    sleep 1
done