title: Return row only if value doesn't exist
body: <p>I have 2 tables - <code>reservation</code>:</p>
  
  <pre><code>   id  | some_other_column
     ----+------------------
     1   | value
     2   | value
     3   | value
  </code></pre>
  
  <p>And second table - <code>reservation_log</code>:</p>
  
  <pre><code>   id  | reservation_id | change_type
     ----+----------------+-------------
     1   | 1              | create
     2   | 2              | create
     3   | 3              | create
     4   | 1              | cancel
     5   | 2              | cancel
  </code></pre>
  
  <p>I need to select only reservations NOT cancelled (it is only ID 3 in this example).
  I can easily select cancelled with a simple <code>WHERE change_type = cancel</code> condition, but I'm struggling with NOT cancelled, since the simple <code>WHERE</code> doesn't work here.</p>