Rails - how to add an Index to a database that sorts by 2 where clauses

I have the following:

      @count = current_user.participations.joins(:topic).where("topic.status = ? AND pa开发者_如何学JAVArticipations.status = ?","open","unread").count

Right now I have an index for:

• topic.status
• participations.status

1 for each table, Do I need to add an index that combines both to optimize this query?

You would need to add an index on each column. I don't believe you can combine columns from separate tables within a single index.