title: Number of times a nested query is executed
body: <p>How many times will this nested sub-query be executed?</p>
  
  <pre><code>SELECT CID, CNAME 
    FROM CUSTOMER
   WHERE EXISTS ( SELECT CID 
                    FROM RENTALS 
                   WHERE CUSTOMER.CID = RENTALS.CID 
                     AND PICKUP = 'CARY' )
  </code></pre>
  
  <p>This is a theoretical question i.e. it is found in my book. The provided answer was 6, but I don't understand why this is so.</p>
  
  <hr>
  
  <p>Ok, I think there is some problem with the book itself. I will go through the book and maybe, later ask the question.</p>