title: How to rollback an update in PostgreSQL
body: <p>While editing some records in my PostgreSQL database using sql in the terminal (in ubuntu lucid), I made a wrong update.</p>
  
  <p>Instead of -</p>
  
  <pre><code>update mytable set start_time='13:06:00' where id=123;
  </code></pre>
  
  <p>I typed -</p>
  
  <pre><code>update mytable set start_time='13:06:00';
  </code></pre>
  
  <p>So, all records are now having the same start_time value.</p>
  
  <p>Is there a way to undo this change? There are some 500+ records in the table, and I do not know what the start_time value for each record was</p>
  
  <p>Is it lost forever?</p>