2 Quick SQL Questions: Paginate Conditions and Adding to Value

I have 2 quick SQL questions that all my googling couldnt come up with an answer

1. Paginate results based on 2 conditions

I currently have sorthelper sorting based on title/author. I'd like the option to select based on 3 genres then be able to sort that through those results by title. I haven't be able to see how to handle sorting with a variable condition. (codes below

2. How to add to current value

How would I add to a current value in my table?

value = value.current + value.new

def upcoming

   items_per_page = 8    @total = Albums.count    @sorter = SortingHelper::Sorter.new self, %w(artist album votes_count date created_at), @params['sort'], @params['order'], 'created_at', 'asc'    @albums_pages, @albums = paginate :albumss, :order => @sorter.to_sql, :per_page => items_per_page

   render :layout => 'albums_upcoming'

end