title: Postgresql delete multiple rows from multiple tables
body: <p>Consider 2 or more tables:</p>
  
  <pre><code>users (id, firstname, lastname)
  orders (orderid, userid, orderdate, total)
  </code></pre>
  
  <p>I wish to delete all <strong>users</strong> and their <strong>orders</strong> that match first name '<strong>Sam</strong>'. In mysql, I usually do left join. In this example userid is unknown to us.</p>
  
  <p>What is the correct format of the query?</p>