Query: ons_notification_topic_by_subscription

select
  case
    when s.id is null then 'no subscriptions'
    else 'with subscriptions'
  end as status,
  count(distinct t.topic_id)
from
  oci_ons_notification_topic t
  left join oci_ons_subscription s on t.topic_id = s.topic_id
group by
  status;