How to send out one email per-day if some content is in review state

I can't seem to figure this out. What I want to do is have an email sent to each of the sites editors once per day if any content is in our review state.

I can create a rule that fires on the node save and checks the moderation state. But this would send out a separate email for every node this occurred on which could get annoying for editors. They need only be reminded once a day.

I take it I need a component that:

• Queries for nodes in review
• If one or more exists then
• Send one email to editors

I would then add this to Rules scheduler which would execute it once per-day. Its the first part: "Queries for nodes in review", that I am stuck on.