title: Finding the hash value of a row in postgresql
body: <p>Is there a way to get the hash code of a row in postgresql? </p>
  
  <p>I need to  export some data only if there is some changes in the data after the last export, the last exported data rows can be stored in a table, the when the again I need to export the data I can get the hash values of all the data and export only those rows who has a different hash value than the last export.</p>
  
  <p>Is it possible to achieve using postgresql?</p>
  
  <p>Thank you</p>