title: Converting a DATE to DATE in UTC time : sys_extract_utc behaving differently for sysdate and systimestamp
body: <pre><code>select sysdate from dual;    
  15-NOV-2018 23:09:31
  
  select cast(sysdate as TIMESTAMP) from dual;
  15-NOV-18 11.07.47.000000000 PM
  
  select sys_extract_utc(cast(sysdate as TIMESTAMP)) from dual;
  15-NOV-18 05.40.35.000000000 PM
  </code></pre>
  
  <p>But,</p>
  
  <pre><code>select systimestamp from dual;
  15-NOV-18 11.11.16.345959000 PM -08:00
  
  select sys_extract_utc(systimestamp) from dual;
  16-NOV-18 07.08.49.772214000 AM
  </code></pre>
  
  <p>Further,</p>
  
  <pre><code>select cast(sysdate as TIMESTAMP) at time zone 'UTC' from dual;
  15-NOV-18 05.48.11.000000000 PM UTC
  </code></pre>
  
  <p>Why is <code>sys_extract_utc(cast(sysdate as TIMESTAMP))</code> different than <code>sys_extract_utc(systimestamp)</code> in my db?
  <br> The time given by <code>sys_extract_utc(systimestamp)</code> is the correct UTC time, btw.
  <br><br> My core requirement is converting data from a table with a DATE column to "DATE in UTC time zone" in a select query. It is of course not working (with either <code>sys_extract_utc</code> or with <code>at time zone 'UTC'</code>), which is probably because of the same reason the above conversion with sysdate is not working.</p>
  
  <p>In case it helps, dbtimezone is:</p>
  
  <pre><code>SELECT DBTIMEZONE FROM DUAL;
  +00:00
  </code></pre>