Dynamic query with left join
Here is the documentation on joins which should put you on the right path to answering the question.
Untested, but something like this should work:
$query = db_select('node', 'n');
$query-&gt;join('comment', 'c', 'n.nid = c.nid');
$query
  -&gt;fields('n', array('nid', 'title'))
  -&gt;condition('n.type', 'page')
  -&gt;condition('n.status', '1')
  -&gt;orderBy('n.created', 'DESC')
  -&gt;addTag('node_access');