title: Is a semi join considered a left or right join?
body: <p>This is a really basic question, but is a semi-join the same as a left or a right join?</p>
  
  <p>That is: when someone says</p>
  
  <blockquote>
    <p>Lets show all users by country. We need to do a semi-join because some countries have no users</p>
  </blockquote>
  
  <p>Does he refer to just doing either a left or right join?</p>