title: Check constraint with condition
body: <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>