orresponds to a <em>many-at-most-one</em> relationship</li>
</ul></li>
</ul></li>
<li>But what happens when we delete or update a row in the table the FK refers to?
<ul>
<li>If the value the FK column(s) refers to doesn’t exist anymore, what do we do?</li>
</ul></li>
<li>In the SQL standards, the valid actions are
<ul>
<li><code>RESTRICT</code>, <code>CASCADE</code>, <code>SET NULL</code>, <code>NO ACTION</code> and <code>SET DEFAULT</code></li>
</ul></li>
<li>Not all valid actions are implemented in all 