Je pense que le date_trunc function peut être votre ami (voir docs postgres ). Vous feriez quelque chose comme ça, je suppose :
select
COUNT(ID) as Total,
COUNT(CASE WHEN createddate between date_trunc('month', now()) AND now() THEN AG.ID END) as ThisMonth,
COUNT(CASE WHEN createddate between date_trunc('month', now()) - interval '1 month' AND date_trunc('month', now()) - interval '1 day' THEN AG.ID END) as LastMonth,
etc...
