title: Converting Relational Algebra to corresponding SQL Query
body: <p>I am trying to understand how to convert properly from <strong>Relational Algebra</strong> into <strong>SQL queries</strong></p>
  
  <p>I find this is one of the things I struggle to convert between. Would anyone be able to share any tips?</p>
  
  <p>Tables: </p>
  
  <pre><code>Room(_roomId_, numberOfBeds, price)
  
  Guest(_guestId_, homeTown, age)
  
  Reservation(_roomId_, _guestId_, date)
  </code></pre>
  
  <p>Relational Algebra: </p>
  
  <pre><code>Πprice(ΠroomId(ΠguestId(σage&lt;20)Guest) Natural Join Reservation) Natural Join Room
  </code></pre>
  
  <p>Query: 
  I managed to deduce the following from part of the statement:</p>
  
  <pre><code>SELECT roomId FROM (SELECT guestID from Guest WHERE age&lt;20) Natural Join Reservation
  </code></pre>
  
  <p>Am I close?</p>