Postgresql sql to get all dates in a range even if there's no date, filling it in

gererate-date-series.sql

with days as (
	select * 
	from generate_series(
		(select min(created_at::date) from visits),
    	(select max(created_at::date) from visits),
    	'1 day'
	) day
) 
select d.day, count(distinct v.ip) 
from days d 
	left join visits v on v.created_at::date = d.day 
group by d.day 
order by d.day ;

-- By hour
with hours as (
	select to_char(hour, 'YYYY-MM-DD HH24') as hour 
	from generate_series(
		(select min(created_at) from visits),
		(select max(created_at) from visits),
		'1 hour'
	) hour
)
select (h.hour || ':00')::timestamp as hour, count(distinct v.ip) 
from hours h left join visits v on to_char(v.created_at, 'YYYY-MM-DD HH24') = h.hour
group by h.hour 
order by h.hour ;