Time histogram helper function

time_histogram.sql

CREATE OR REPLACE FUNCTION time_histogram(
	start_time timestamp, 
	end_time timestamp
)
RETURNS TABLE(bucket timestamp) AS $$
DECLARE diff_hours int;
BEGIN
	
	diff_hours = abs(extract(epoch from end_time - start_time) / 3600)
	raise notice 'diff hours: ', diff_hours;  

	if diff_hours <= 1 then
	
		select generate_series(
			date_trunc('minute', start_time),
			date_trunc('minute', end_time),
			'1 minute'::interval
		) as bucket
		;
		
	else if diff_hours <= 24 then

		select generate_series(
			date_trunc('minute', start_time),
			date_trunc('minute', end_time),
			'15 minutes'::interval
		) as bucket
		;
		
	else if diff_hours <= (24 * 7) then

		select generate_series(
			date_trunc('hour', start_time),
			date_trunc('hour', end_time),
			'1 hour'::interval
		) as bucket
		;

	end if;

END;
$$ LANGUAGE psql;

select * from time_histogram(
	'2020-04-06 08:30:46.85378'::timestamp, 
	'2020-12-08 15:04:00.516976'::timestamp
);

drop function if exists time_histogram;