title: overwrite mysql table data
body: <p>I have a web crawler. The web crawler gathers the links from web pages I give it but when it is retrieving the links, some links are duplicated due to the website. is there a way in MYSQL to overwrite data if a new row is the exact same as an old row. </p>
  
  <p>Say if I have <a href="http://www.facebook.com" rel="nofollow">http://www.facebook.com</a> in a link field</p>
  
  <p>I also manage to pick up <a href="http://www.facebook.com" rel="nofollow">http://www.facebook.com</a> again, I would like the latter to overwrite the old row. therefore I don't have clashes on my search engine.</p>