title: SQL query for finding countries in the world with 3 times bigger population than all of the countries at the same continent
body: <p>I have a table which name is 'world'. That table has columns in this order: name, continent, area, population and gdp. The query i want to write is for the next problem:
  Some countries have populations more than three times that of any of their neighbours (in the same continent). Give the countries and continents.</p>
  
  <p>My query is like this:</p>
  
  <pre><code>SELECT 
      name, continent 
  FROM 
      world as x
  WHERE
      x.population/3 &gt; ALL (SELECT population 
                            FROM world as y 
                            WHERE x.continent = y.continent)
  </code></pre>
  
  <p>But it doesn't work as it is supposed to. What can be the possible problem?</p>