SQL query complex relay

First of all, the user has a lot of age_demographics. The AgeDemographic object looks like this:

#<AgeDemographic id: 4384, user_id: 799, range: "35 - 49", percentage: 3.2, created_at: "2015-05-22 04:17:10", updated_at: "2015-05-22 04:17:10">

      

        
        
        
      

    

I am creating a user search tool where someone will select multiple age ranges that they want to target (like "12 - 17"

and "18 - 24"

). I need to select users who have a collection of age demographics with a total percentage greater than 50%

.

This is what I started with:

 User.joins(:age_demographics).where("age_demographics.range IN (?)", ["12 - 17", "18 - 24", "25 - 34"])

      

        
        
        
      

    

But I can't figure out how to link the sum of the percentages of these age_demographics to this where clause.

Let me know if this doesn't make any sense.