title: Liquibase drop constraint without knowing it's name
body: <p>We use liquibase to keep track of our database changes..
  First changeSet contains those lines:</p>
  
  <pre><code>&lt;column name="SHORT_ID" type="INTEGER"&gt;
     &lt;constraints unique="true" /&gt;
  &lt;/column&gt;
  </code></pre>
  
  <p>Basically it means that SHORT_ID column has unique constraint but the name of this constraint can be whatever and usually is different each time (we run some integration tests against H2 databases and new bases are made each time we run tests)</p>
  
  <p>So.. problem is: I can't change this first changeSet but now we have to get rid of this unique constraint. Any ideas how to achieve that by using liquibase?  </p>