A stored PostgreSQL function to generate time range series. Join your data to the function's result and group by date_from in order to build a time-series histogram without gaps even if there is no data in some time ranges.

no_gaps_time_ranges.sql

CREATE OR REPLACE FUNCTION no_gaps_time_ranges(
  in start_date timestamptz,
  in interval_len_sec bigint,
  in num_intervals bigint
)
RETURNS TABLE (date_from timestamptz, date_to timestamptz)
LANGUAGE plpgsql
IMMUTABLE
AS $function$
DECLARE
  abs_interval_len_sec bigint;
  seconds_start bigint;
  seconds_start_boundary bigint;
  series_from bigint;
  series_to bigint;
BEGIN

abs_interval_len_sec = abs(interval_len_sec);
	
select trunc(extract(epoch from start_date))::bigint into seconds_start;
-- raise notice 'seconds_start = %', seconds_start;

select seconds_start - mod(seconds_start,interval_len_sec) into seconds_start_boundary;
-- raise notice 'seconds_start_boundary = %', seconds_start_boundary;

if interval_len_sec < 0
then -- going backwards
  series_from = seconds_start_boundary + num_intervals * interval_len_sec;
  series_to = seconds_start_boundary + interval_len_sec;
else -- going forward
  series_from = seconds_start_boundary;
  series_to = seconds_start_boundary + (num_intervals-1) * interval_len_sec;
end if;
--raise notice 'series: from = %, to = %', series_from, series_to;

return query
with sec_thresholds as (
  select generate_series(series_from, series_to, abs_interval_len_sec) as sec_thr
)
select
  to_timestamp(sec_thr) as date_from,
  to_timestamp(sec_thr + abs_interval_len_sec) as date_to
from sec_thresholds;
return;
END;
$function$