[Solved]-Rails ActiveRecord group_by & sum db results for use with Lazy HighCharts-Highcharts

It looks like you have everything in place. Here's how you can pull data from db:

@aggregated_invoices = Invoice.
  where(:account_id => params[:id]).
  order("invoice_date DESC").
  group("invoice_date").
  select("DATE_FORMAT(invoice_date, '%Y-%m-01') AS invoice_date, sum(amount_used) AS amount_used, sum(billed_amount) AS billed_amount")

# Then use these instead of sample data:
@categories = @aggregated_invoices.map {|i| i.invoice_date.strftime("%b/%Y")}
@amount_used_data = @aggregated_invoices.map(&:amount_used)
@billed_amount_data = @aggregated_invoices.map(&:billed_amount)