(PHP 4 <= 4.1.0, PECL dbplus >= 0.9)
dbplus_update — Update specified tuple in relation
$relation
   , array $old
   , array $new
   )
   dbplus_update() replaces the old
   tuple with the data from the new one, only if the
   old completely matches a tuple within
   relation.
  
This function is EXPERIMENTAL. The behaviour of this function, its name, and surrounding documentation may change without notice in a future release of PHP. This function should be used at your own risk.