title: Is there a PHP function or method to do a checksum on data?
body: <p>I have a MySQL database I am working on in PHP where It will perform address verification from a daily data feed. We would do address correction on our end, because we don't have control over the source of the feed.</p>
  
  <p>I am trying to come up with a method to see if the address has been changed at the source. If it changes then an address verification would be performed in PHP on our MySQL database.</p>
  
  <p>Without storing a copy of the old feed I was thinking it might be better to do a checksum of the fields from the feeds and store this with each record. Then each feed after that it would see if the checksum has changed. Is this the best method to do this? Might there been a PHP function to do all this already? What about something in MySQL? Thanks!</p>