I'm using rails 3.0 and MySql 5.1

I have these three models:

Question, Tag and QuestionTag.

Tag has a column called name.

Question has many Tags through QuestionTags and vice versa.

Suppose I have n tag names. How do I find only the questions that have all n tags, identified by tag name.

And how do I do it in a single query.

(If you can convince me that doing it in more than one query is optimal, I'll be open to that)

A pure rails 3 solution would be preferred, but I am not adverse to a pure SQL solution either.