title: what is this order by 1?
body: <p>I had a question in MySQL, did it correctly. But the book code differs a little.</p>
  
  <p>Book:</p>
  
  <pre><code>use tennis;
  select playerno, datediff(coalesce(end_date, current_date), 
  begin_date) as Difference, position
  from committee_members
  where datediff(coalesce(end_date, current_date), begin_date) &gt; 500
  order by 1;
  </code></pre>
  
  <p>What is this order by 1 ? </p>
  
  <p>My code also works and is almost the same except:</p>
  
  <pre><code>select playerno, datediff(coalesce(end_date, current_date) AS Data,
  order by Data;
  </code></pre>