Catching different unique keys in MySQL

[Kings]

I was hoping someone will be able to help me with the following. I've got a table that looks like this:

CREATE TABLE `user` (
  `userid` mediumint(9) NOT NULL auto_increment,
  `email` varchar(255) NOT NULL default '',
  `customerid` varchar(255) NOT NULL default '',
  PRIMARY KEY  (`userid`),
  UNIQUE KEY `customerid` (`customerid`),
  UNIQUE KEY `email` (`email`)
) TYPE=MyISAM AUTO_INCREMENT=1 ;

As you can see it has two unique keys and a primary key. I've added the unique keys because I want the customerid and the e-mail address to be unique.

In most situations my tables only have one unique key, so I can something like this to catch the unique error and handle it:

$db->exec ("INSERT INTO table (field1, field2) VALUES ('one', 'dup')");

if ($db->errno == 1062) {
echo 'Already exists, please go back and try a different one';
}

// ... 

But how would I do this with two unique keys, and be able to know which key triggered the unique error?

MySQL does return the key number, like so:

Duplicate entry 'foo' for key 3

But that isn't really helpful, since I have no real way of knowing what key 3 or key 2 is. I'd rather have the actual fieldname. Another problem is that I'd have to parse the error message.

Any suggestions or tips? Or should I just hard code the key 3 and key 2 in my script?

[Kings]

I've solved it already. I pretty much went with my original thought (hardcode the key numbers and parse the error message), but it's all abstracted away in my DB library, so I can do this:

if ($crud->user->unique_error('customerid') == true) {
echo 'CustomerID is not unique';
die();
}

if ($crud->user->unique_error('email') == true) {
echo 'E-mail address is not unique';
die();
} 

Works perfectly!