title: unique constraint check not enforced
body: <pre><code>create table A (id, field1, field2, field3, field4)
  </code></pre>
  
  <p>I have a <code>unique constraint on field1, field2, field3</code> and the following records are stored in the table</p>
  
  <p>e.g.</p>
  
  <pre><code>insert into A (1, "f1", null, "f3", "f4");
  insert into A (2, "f1", null, "f3", "f4");
  insert into A (3, "f1", null, "f3", "f4");
  </code></pre>
  
  <p>I would expect this to throw an unique constraint violation since all records are in violation, but it doesn't. What am I missing here, did check the database and the unique constraint index has been created.</p>