title: Whoosh: shouldn't OR only increase results?
body: <p>We have about 9k documents indexed using Haystack 1.2.7 with Whoosh 2.4.1 as backend. Despite of using Haystack, it looks like a Whoosh problem. Take a look at my debug cases:</p>
  
  <p>1) If I just run an exact lookup, Whoosh finds my document (as below):</p>
  
  <pre><code>&gt;&gt;&gt; SearchQuerySet().all().models(PedidoSaida).filter(numero__exact='6210202443/10')
  [&lt;SearchResult: logistica.pedidosaida (pk=u'6')&gt;]
  </code></pre>
  
  <p>2) If I just run a startswith lookup, Whoosh doesn't find my document (as below):</p>
  
  <pre><code>&gt;&gt;&gt; SearchQuerySet().all().models(PedidoSaida).filter(numero__startswith='6210202443/10')
  []
  </code></pre>
  
  <p>3) If I put all together in a single OR query, Whoosh still doesn't find my document (as below):</p>
  
  <pre><code>&gt;&gt;&gt; SearchQuerySet().all().models(PedidoSaida).filter(SQ(numero__exact='6210202443/10') | SQ(numero__startswith='6210202443/10'))
  []
  </code></pre>
  
  <p>Taking a look into the queries that Haystack sends to Whoosh, we have:</p>
  
  <pre><code>&gt;&gt;&gt; str(SearchQuerySet().all().models(PedidoSaida).filter(numero__exact='6210202443/10').query)                                       
  '(numero:6210202443/10) AND (django_ct:logistica.pedidosaida)'
  
  &gt;&gt;&gt; str(SearchQuerySet().all().models(PedidoSaida).filter(numero__startswith='6210202443/10').query)
  '(numero:6210202443/10*) AND (django_ct:logistica.pedidosaida)'
  
  &gt;&gt;&gt; str(SearchQuerySet().all().models(PedidoSaida).filter(SQ(numero__exact='6210202443/10') | SQ(numero__startswith='6210202443/10')).query)
  '((numero:6210202443/10 OR numero:6210202443/10*)) AND (django_ct:logistica.pedidosaida)'
  </code></pre>
  
  <p>As you can observe, the last query is exactly (first OR second). Shouldn't Whoosh find my document? I can't see where my logic is wrong: I'm using OR and it is finding less than when I use one of the statements.</p>
  
  <p>I also think it is weird that Whoosh finds my document with the first query (numero:6210202443/10), but not with the second (numero:6210202443/10*) one. But I guess it has to do with StemmingAnalyzer that Haystack uses in my CharField. I'll take a deep look into that after.</p>