drupal/modules/comment/comment.install

<?php
// $Id$

/**
 * Implementation of hook_enable().
 */
function comment_enable() {
  // Insert records into the node_comment_statistics for nodes that are missing.
  db_query_temporary("SELECT n.nid, n.created, n.uid FROM {node} n LEFT JOIN {node_comment_statistics} c ON n.nid = c.nid WHERE c.comment_count IS NULL", 'missing_nids');
  db_query("INSERT INTO {node_comment_statistics} (nid, last_comment_timestamp, last_comment_name, last_comment_uid, comment_count) SELECT n.nid, n.created, NULL, n.uid, 0 FROM missing_nids n");
}