title: Propel subqueries in select
body: <p>I need  to find article from database, and also the next and previous id of the neighbours.
  Right now i have 3 queries that work - first two are without the find() method - i know that.</p>
  
  <pre><code>$artNext = ArticlesQuery::create()
              -&gt;filterById(array('min' =&gt; $artId + 1))
              -&gt;filterByActive(1)
              -&gt;filterByType(1)
              -&gt;select('Id')
              -&gt;orderById(Criteria::ASC)
              -&gt;limit(1);
  
  
  $artPrev = ArticlesQuery::create()
              -&gt;filterById(array('max' =&gt; $artId - 1))
              -&gt;filterByActive(1)
              -&gt;filterByType(1)
              -&gt;select('Id')
              -&gt;orderById(Criteria::DESC)
              -&gt;limit(1);
  
  
  $article = ArticlesQuery::create()
              -&gt;filterByActive(1)
              -&gt;filterById($artId)
              -&gt;findOne();
  </code></pre>
  
  <p>How can i combine artPrev and artNext subqueries to be inserted as in the following query (simplified)</p>
  
  <pre><code>select id,
  (select id from articles where id&lt;77 ORDER BY id DESC limit 1 ) as prev,
  (select id from articles where id&gt;77 ORDER BY id ASC limit 1) as next
  from articles 
  where id=77
  </code></pre>