Rails Equivalent of SQL - ruby-on-rails

Question

Given the following models:
class PeriodBilling < ActiveRecord::Base
belongs_to :appcode
belongs_to :period
belongs_to :sla
belongs_to :unit_type
belongs_to :dpc_employee
belongs_to :general_ledger
end
class GeneralLedger < ActiveRecord::Base
has_many :appcodes
has_many :sla_task_details
belongs_to :expense_category
has_many :period_billings
has_many :expected_billings
end
How would I find the following SQL equivalent in Rails, to display as a matrix with periods down the left side and general_ledgers across the top, with the sum(pb.current_amt) in the appropriate fields?
select pb.pe_number, gl.general_ledger_number, sum(pb.current_amt)
from period_billings pb, general_ledgers gl
where pb.sla_id = 21
and pb.general_ledger_id = gl.id
group by pb.pe_number, gl.general_ledger_number
In Active Record terms, this is kinda what I'm trying to find:
#sla = Sla.find(params[:id])
#period_billings = PeriodBilling.where("sla_id = ?", #sla.id).group_by(&:general_ledger_id)
#billing_sum = #period_billings.inject(0){|sum,billing| sum+billing.current_amt}
So, I want to find all period_billings for the selected sla, grouped by general_ledger_id to get the sum of the period_billing.current_amt for those records. Then, I want to put the 12 periods down the side to show the summed amount in its appropriate general_ledger column across the top.
Thanks in advance!!! :)

Answer 1

Just a wild little stab at what I suggest you do. Some things are better meant for direct sql, and when that arises, like you're requesting, it's best to just use sql.
ActiveRecord::Base.connection.execute <<-EOF
select pb.pe_number, gl.general_ledger_number, sum(pb.current_amt)
from period_billings pb, general_ledgers gl
where pb.sla_id = 21
and pb.general_ledger_id = gl.id
group by pb.pe_number, gl.general_ledger_number
EOF