$query = "INSERT IGNORE INTO `user` (`name`, `email`) VALUES ( '".$name."', '".$email."')";
$res = mysql_query($query) or die("Query failed ".mysql_error() );
$last id = mysql_insert_id();
mysql_insert_id() return 0 if there is a duplicated entry.
Is there a way to get the ID of the duplicated entry ? or do I have to do 2 query ( SELECT + INSERT ) ?