[Exim] Mysql issues

Hello,

I currently use Exim 3.03 with files (lsearch) to store the localdomains, system aliases, virtual aliases,etc...
I'm configuring Exim 3.16 to use Mysql database to ease the management of the email accounts (i.e. manage it on a web interface using PHP4).

My first question : Does Mysql decrease the performance of Exim through the database queries, etc... ?

My second question is about my configure file. I've taken the working configure file which is using lsearch. I've tried to modify it to make it work with Mysql.
My Mysql database is called Exim, the user that has access to this database is admin, and the password is test.
The table localdomains has a unique field, name, which is a local domain.

For the local_domains statement, I've used the following:

mysql_servers = localhost/exim/admin/test
local_domains = localhost:mysql;select namefrom localdomains

Although I don't get any error message when I run exim, it return a Mail delivery message when I test it.
What's wrong?

cheers
Guillaume