title: What does this UN mean?
body: <p>I wanted to do an insert into with a union, and someone suggested this:</p>
  
  <pre><code>SELECT x INTO ##temp
  FROM (SELECT x FROM y UNION ALL SELECT x FROM z) UN
  </code></pre>
  
  <p>It works, but what is the <code>UN</code>? Unfortunately, Googling for "t-sql un" isn't very helpful :p</p>
  
  <p>Note: I found out that you can just do <code>SELECT x INTO ##temp FROM y UNION ALL SELECT x FROM b</code> but I'm still curious about <code>UN</code>.</p>
  
  <p>EDIT: Ok, so it's an alias, but why is it required to make this work? If I remove it, it won't execute.</p>