[Exim] MySQL Quicky

Can anyone see any reason as to why the following router would not work.

virtual_router:
driver = domainlist
route_list = mysql;SQL_LOCAL_DOMAIN
transport = virtual_delivery

SQL_LOCAL_DOMAIN = SELECT DISTINCT MYSQL_DOMAINFIELD FROM MYSQL_AUTHTABLE
WHERE MYSQL_DOMAINFIELD LIKE '$key'

I have probably missed something fundamental.

Cheers

Andy