Check constraint with condition
<p>I'm wondering if this condition can be done by a check constraint or do I need to create a trigger.</p>

<p>Condition : if student admited date is not null then exam mark is null</p>

<p><strong>Remark: Constaint case OR Trigger</strong> </p>

<p><strong>What I tried :</strong></p>

<pre><code>ALTER TABLE ADMITED_TABLE
ADD CONSTRAINT AAAA CHECK
 ( CASE  WHEN  DATEADMITED IS NOT NULL THEN MARK NULL END);
</code></pre>

<p><strong>Error:</strong></p>

<pre><code>ORA-00920: invalid relational operator
00920. 00000 -  "invalid relational operator"
</code></pre>