title: MySQL query select rows from table according to specific key that is not in another table
body: <p>How to select all exams by its ID and title (from table 'exams'), that a student (in table 'grades') hasn't written yet?</p>
  
  <p>TABLE: grades</p>
  
  <pre><code>+--------------+----+----
  |student_number|e_id| ...
  +--------------+----+----
  |888075        |1   | ...
  |888075        |2   | ...
  |888075        |4   | ...
  |637020        |2   | ...
  +--------------+----+----
  </code></pre>
  
  <p>TABLE: exams</p>
  
  <pre><code>+----+------+
  |e_id|title |
  +----+------+
  |1   |exam 1|
  |2   |exam 2|
  |3   |exam 3|
  |4   |exam 4|
  +----+------+
  </code></pre>
  
  <p>In this particular case I would expect the following output for student <code>888075</code>:</p>
  
  <pre><code>+--+------+
  |id|title |
  +--+------+
  |3 |exam 3|
  +--+------+
  </code></pre>
  
  <p>I just need the inverse selection of this:</p>
  
  <pre><code>SELECT e.e_id as id, e.title as title
  FROM grades g
  LEFT JOIN exams e
  ON g.e_id = e.e_id
  WHERE g.student_number = '888075'
  </code></pre>