Combine sql with ferret

Dear all,
   Ferret seems to be great for full text searches and mysql is
suitable for relational searches. Now, what is the most efficient way
to combine both in a ruby on rails application? For instance, I would
like to retrieve all entries matching a lucene query AND a mysql
   Thank you for your help,

No way to combinate directly i think.

But you can make one as a filter to another one.