title: What happens to JOIN if no colums from said table are SELECT-ed?
body: <p>I am wondering how Oracle, or how DB managers, work through longer scripts and bigger result. I will give an example and some questions below:</p>
  <pre><code>SELECT order.nr, order.date, order.datesent, items.id, items.name
  FROM orders
    LEFT JOIN items ON orders.itemid=items.id
    LEFT JOIN customer ON orders.custid=customer.id
    LEFT JOIN shipper ON order.shipperid=shipper.id
    LEFT JOIN production ON production.itemid=items.id
    LEFT JOIN sales ON sales.orderid=orders.id
    LEFT JOIN transport ON orders.transid=transport.id
  </code></pre>
  <ul>
  <li>Does the script run through all tables even though I don't use them in the SELECT?</li>
  <li>Generally does this slow down the script execution if it brings back a lot of data?</li>
  </ul>