title: sql -> relational algebra
body: <p><img src="https://i.stack.imgur.com/Jobvg.png" alt="enter image description here"></p>
  
  <p>How do I convert this to relational algebra tree?</p>
  
  <p>What are the logical steps? Do I first need to convert to relational algebra? Or can I go straight from sql to tree?</p>