title: Postgres Join and return flag if a row exists
body: <p>I am very certain that this is possible in SQL but I am not sure how to implement this. I am using PostgreSQL</p>
  
  <p>I have 2 tables</p>
  
  <ul>
  <li><code>users</code> with columns id, name and created_date</li>
  <li><code>user_docs</code> with columns id, value</li>
  </ul>
  
  <p>I want to write a select query which returns all <code>users</code> table columns, along with another column called <code>has_docs</code> which indicates whether the user has any document rows in the <code>user_docs</code> table.</p>
  
  <p>Can someone help?</p>