title: Admin, filtering posts list with INNER JOIN
body: <p>I'm developping a Wordpress plugin in witch I have created some custom posts and I use meta datas to link them together.</p>
  
  <p>On the admin side, I want to be able to filter posts list using those relations. I guess I would need to use INNER JOIN but I don't know how.</p>
  
  <p>For now all I have is : </p>
  
  <pre><code>add_filter( 'parse_query', 'mypostsfilteringfunction' );
  function mypostsfilteringfunction( $query ){
  
          // if post_type matches : 
          // then I need to be able to add innerjoin into $query
  
  }
  </code></pre>
  
  <p>Thanks in advance for your help.</p>