title: left join table on itself sql
body: <p>I have a simple sql question here, I see some queries like this:</p>
  
  <pre><code>SELECT 
      users.id, users.username, users.password
  FROM
      users AS User
          LEFT JOIN
      users AS User0 ON ...
          LEFT JOIN
      users AS User1 ON ...
          LEFT JOIN
      users AS User2 ON ...
  WHERE
      ...
  ORDER BY ... DESC
  </code></pre>
  
  <p>In which, as you can see above, the same table <code>users</code> is being left-joined 3 times. My question is this, why would somebody wanna join a table on itself? What exactly is the purpose of doing something like that?</p>
  
  <p>Please give me the best explanation with clear examples if possible</p>
  
  <p>Thank you</p>