ck(end_date &gt;= start_date)</code>
<ul>
<li>note that if any of the dates is <code>null</code>, the expression will be <code>null</code> and the check will pass</li>
</ul></li>
</ul></li>
</ul>
<h3 id="domain-constraints">Domain Constraints</h3>
<ul>
<li>A domain is used to restrict the possible values for a data type</li>
<li>A domain
<ul>
<li>can have a default value</li>
<li>can be defined with a <code>null</code> or <code>not null</code> constraint</li>
<li>can have 1 or more check constraints</li>
</