Verify discount accuracy for a previously invoiced billing period (corrections excluded)

Postgres SQL, as run

select case when publisher_name is not null and publisher_name is distinct from invoice_issuer_name then publisher_name else provider_name end as service_provider_name,
       billing_account_id as billing_account_id,
       billing_account_name as billing_account_name,
       billing_currency as billing_currency,
       service_name as service_name,
       sum(effective_cost) as total_effective_cost,
       sum(list_cost) as total_list_cost,
       sum(billed_cost) as total_billed_cost,
       (sum(list_cost) - sum(effective_cost)) / nullif(sum(list_cost), 0) as effective_discount
from focus.cost_and_usage
where billing_period_start >= $1::timestamptz
  and billing_period_end < $2::timestamptz
  and charge_class is distinct from 'Correction'
group by 1, 2, 3, 4, 5
order by total_list_cost desc nulls last, service_provider_name, billing_account_id, service_name nulls last
limit 500

Parameters: $1 = billing_period_start, $2 = billing_period_end

Original FOCUS SQL

SELECT
  ServiceProviderName,
  BillingAccountId,
  BillingAccountName,
  BillingCurrency,
  ServiceName,
  SUM(EffectiveCost) AS TotalEffectiveCost,
  SUM(ListCost) AS TotalListCost,
  SUM(BilledCost) AS TotalBilledCost,
  ((SUM(ListCost) - SUM(EffectiveCost)) / NULLIF(SUM(ListCost), 0)) * 100 AS EffectiveDiscount
FROM focus_data_table
WHERE BillingPeriodStart >= ? AND BillingPeriodEnd < ?
  AND ChargeClass != 'Correction'
GROUP BY
  ServiceProviderName,
  BillingAccountId,
  BillingAccountName,
  BillingCurrency,
  ServiceName