Inserting/Updating a Flat File Upload

[netfrugal]

The following code I got to insert a tab-delimited text file to mysql.

But, I'm stuck on one part. I can INSERT, but I can't UPDATE. This script simply inserts anything in the text file, but if I accidentally click the refresh button 2x, then I've inserted the data 2x.

The first column in the text file is the unique id for what I'm uploading, which is just 3 columns: id, name, email

Here's what I've hammered out:

<?  

require('db_conn.php');

  $fcontents = file ('files/textfile.txt'); 


  for($i=0; $i<sizeof($fcontents); $i++) { 
      $line = trim($fcontents[$i]); 
      $arr = explode("\t", $line); 


  $sql = "insert into TABLE_NAME values ('". implode("','", $arr) ."')"; 
  mysql_query($sql);
  echo $sql ."<br>\n";
  if(mysql_error()) { echo mysql_error() ."<br>\n";  } 
}
?>

I'd like to try updating the records if I hit submit twice. This would be handy if I decided to change the email record for one of the records.

thanks a ton!