drupal - create arbitrary number of placeholders for a SQL injection resistant db_query() call

gistfile1.php

<?php
$nids = array(1, 2, 3, 4, 5);

// This is the key piece to understand -- it creates as many placeholder as you want based on the length of $nids array.
$placeholders = implode(',', array_fill(0, count($nids), '%d')); 

$results = db_query("
  select r.title
  from {node_revisions} r
  join {node} n
  on r.vid = n.vid
  where n.nid in ($placeholders)
", $nids); // Notice how I think use the $placeholders in the the query.