title: oracle how can check if 'time' not date between two date Fields with time
body: <p>Q1 - i have this task where i want to check if there is no overlap in "time" between two dates fields (start_date , end_date) and their time 
  , the time i want to check is in the same date with the start and end date</p>
  
  <p>any ideas or tips   </p>
  
  <p>Q2 - </p>
  
  <pre><code>select 
      extract( hour from
          to_timestamp(
              to_char('04/04/2018 04:05:05','dd/mm/yyyy hh24:mi:ss')
          )
      ) as v_to 
  from dual;
  </code></pre>
  
  <p>Returns :</p>
  
  <blockquote>
    <p><strong>ora-01722</strong> <em>invalid number</em></p>
  </blockquote>
  
  <p>My NLS_TIMESTAMP_FORMAT is 'DD-MON-YYYY HH24:MI:SS'</p>