title: SQL SELECT Cities
body: <p>I have that homework to write a SQL query that: </p>
  
  <ol>
  <li>Selects countries where a total number of inhabitants (population) in all the cities is greater than 400 </li>
  <li>Selects names of countries that have no buildings at all.</li>
  </ol>
  
  <p>There is a tables definitions</p>
  
  <p><a href="https://i.stack.imgur.com/nasbJ.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nasbJ.jpg" alt="http://imgur.com/hLZZ90F"></a></p>
  
  <p>I)</p>
  
  <pre><code>SELECT c1.Name
  FROM Country c1
  JOIN City c2 ON (c1.CountryID = c2.CountryID)
   WHERE NOT EXISTS 
         (SELECT *
            FROM City
           WHERE Population &lt; 400)
  ;
  </code></pre>
  
  <p>Why isn't this correct ? I'm not getting any records.</p>