title: What is "Correlated Fetch" as talked in Session 214 of WWDC 2012?
body: <p>She was talking about query</p>
  
  <pre><code>ANY tag.searchString == "rome" AND label == "red"
  </code></pre>
  
  <p>"is really better done as a correlated fetch" like this:</p>
  
  <pre><code>ANY tag IN FETCH(%@, %@, NO) AND label == "red"
  </code></pre>
  
  <p>But I've never heard this thing or seen this syntax before, nor can I find them on web. So what's Correlated Fetch and where can I find documents about it?</p>