title: join two tables that may contain no data
body: <p>I have two tables:</p>
  
  <h2>attendance</h2>
  
  <ul>
  <li>attendance_id_pk         </li>
  <li>student_id                   </li>
  <li>is_excused                   </li>
  </ul>
  
  <h2>checking</h2>
  
  <ul>
  <li>checking_id_pk</li>
  <li>student_id</li>
  <li>parent_consent</li>
  </ul>
  
  <hr>
  
  <p>I want to join all data in the attendance table to checking table IF:</p>
  
  <p>is_excused = true and parent_consent = false using student_id. It is possible that attendance table has no data in it. How to do this in postgresql?</p>