group by + sum on multiple columns in rails 3

问题

I need to get a list of locations ordered by the number of picture that I have in the DB for these locations, here is my query

Location.select(:city).group(:city).order("SUM(images_count) DESC").sum(:images_count)

This worked like a charm, unfortunately, I now need to add province and country to prevent ambiguities to arise, so I now have this

Location.select(:city, :province, :country).group(:city, :province, :country).order("SUM(images_count) DESC").sum(:images_count)

And this is not working :(

Could someone help me out with this query?

回答1:

I'm not very proud of my solution but it works:

Location.group(:city, :province, :country)
        .select(:city, :province, :country, "SUM(images_girl_count) as sum_images_count")
        .order("sum_images_count DESC")
        .collect{ |location| [location.city, location.province, location.country, location.sum_images_count] }

Any feedback?

回答2:

The sum method only use one column while grouping, try this :

Location.select(:city, :province, :country, "SUM(images_count) as sum_images_count").group(:city, :province, :country).order("sum_images_count DESC")

It may be a better way though.

I hope it would help.

来源：https://stackoverflow.com/questions/4855821/group-by-sum-on-multiple-columns-in-rails-3