title: Cast timestamp to timestamp with time zone
body: <p>I am trying convert timestamp to timestamp with time zone with adding GMT time zone: </p>
  
  <pre><code>to_timestamp(to_char(t.time_started, 'DD-MON-YYYY hh24:mi:ss')
    || nvl2(t.time_started, ' GMT', null), ('DD-MON-YYYY hh24:mi:ss tzd'))
  </code></pre>
  
  <p>but this gets ORA-01812 date format not recognized. How can I specify add the time zone?</p>