title: Liquibase preconditions with sequenceexists not working
body: <p>I'm trying to run liquibase on existing db, at that i'm facing error sequence already exists</p>
  
  <pre><code>&lt;createSequence sequenceName="call_id_seq" schemaName="dw"/&gt;
  </code></pre>
  
  <p>after i tried with preConditions, its not working as expected. I,m new to this liquibase,any one could you please suggest on this</p>
  
  <pre><code>&lt;changeSet author="ashok" id="1443436437214-1"&gt;
      &lt;preConditions onFail="MARK_RAN"&gt;
          &lt;not&gt;
              &lt;sequenceExists sequenceName="call_id_seq" schemaName="dw"/&gt;
          &lt;/not&gt;
      &lt;/preConditions&gt;
      &lt;createSequence sequenceName="call_id_seq" schemaName="dw"/&gt;
  &lt;/changeSet&gt;
  </code></pre>