Query: compute_instance_by_creation_month

with instances as (
  select
    title,
    time_created,
    to_char(time_created,
      'YYYY-MM') as creation_month
  from
    oci_core_instance
  where
    lifecycle_state <> 'TERMINATED'
),
months as (
  select
    to_char(d,
      'YYYY-MM') as month
  from
    generate_series(date_trunc('month',
        (
          select
            min(time_created)
            from instances)),
        date_trunc('month',
          current_date),
        interval '1 month') as d
),
instances_by_month as (
  select
    creation_month,
    count(*)
  from
    instances
  group by
    creation_month
)
select
  months.month,
  -- instances_by_month.count
  coalesce(instances_by_month.count, 0)
from
  months
  left join instances_by_month on months.month = instances_by_month.creation_month
order by
  months.month desc;