title: How to update Oracle Timestamp value from the current to a timestamp from the past
body: <p>I have an Oracle Table called <code>EVENT_TABLE_T</code>. It has a column called <code>LAST_UPDATE_DT</code>. One sample value from this column is: <code>01-JUL-13 11.20.22.37448900 AM</code>. There are over 700 rows that have this same timestamp value.
  I would like to update this value to 45 days before this date, using a SQL statement.
  For example,<code>01-JUL-13 11.20.22.37448900 AM</code>, after my mental arithmetic, should become: <code>15-May-13 11.00.00......</code> (exactly 45 days).
  If this is successful, I would like to apply an update on a different value in <code>LAST_UPDATE_DT</code> that reflects a value that goes back back 46 days.</p>
  
  <p>What I hope to accomplish by asking this question is to be able to learn the basics of Oracle dates and timestamps and apply them to my batch processing work.
  I would like to be able to run this update sql statement from Oracle SQL Developer and also from inside a Java <code>PreparedStatement.</code></p>
  
  <p>Thanks in advance for your help.</p>