title: select from union of two tables
body: <p>I have two tables <code>Cars2016</code> and <code>Cars2015</code>, which have exactly the same columns.</p>
  
  <p>I want to simply concatenate these two tables to create this kind of query :</p>
  
  <pre><code>SELECT Mark, COUNT(Models) FROM (Cars2015 UNION Cars2016) GROUP BY Mark
  </code></pre>
  
  <p>This query aims to know for each mark how many models it has, cumulating year 2015 and year 2016.</p>
  
  <p>How can I do that <strong>efficently</strong> ?</p>
  
  <p>Thanks !</p>