intersect date intervals and calculate value within them - postgresql

Question

I have a table containing "start_at", "finish_at" and "value" columns:
start_at
finish_at
value
2022-11-01 10:00:00
2022-11-01 22:00:00
5
2022-11-01 16:00:00
2022-11-01 19:00:00
8
2022-11-01 18:00:00
2022-11-01 23:00:00
3
I want to aggregate date intervals and calculate max value within them. Expected result:
start_at
finish_at
max
2022-11-01 10:00:00
2022-11-01 16:00:00
5
2022-11-01 16:00:00
2022-11-01 19:00:00
8
2022-11-01 19:00:00
2022-11-01 22:00:00
5
2022-11-01 22:00:00
2022-11-01 23:00:00
3
I tried SELECT range_agg(tsrange(start_at, finish_at)), max(value) FROM my_table; but the result is not exactly what I need:
range_agg
max
{["2022-11-01 10:00:00","2022-11-01 23:00:00")}
8

Answer 1

setup.
BEGIN;
CREATE TABLE test6 (
start_at timestamp,
finish_at timestamp,
value numeric
);
INSERT INTO test6
VALUES ('2022-11-01 10:00:00', '2022-11-01 22:00:00', 5),
('2022-11-01 16:00:00', '2022-11-01 19:00:00', 8),
('2022-11-01 18:00:00', '2022-11-01 23:00:00', 3);
CREATE VIEW test6v AS
SELECT
tsrange(start_at, finish_at, '[)'),
value
FROM
test6;
COMMIT;
query:
WITH cte AS (
SELECT
tsrange(s, s + interval '3 hour', '[)') AS RANGE
FROM (
SELECT
generate_series(min(start_at), max(finish_at), interval '3 hour')
FROM
test6) foo (s))
SELECT
RANGE,
max(value) FILTER (WHERE RANGE && tsrange IS TRUE)
FROM
cte
CROSS JOIN test6v
GROUP BY
RANGE
ORDER BY
RANGE;
You can customize your desired interval range table. here I slice min(start_at), max(finish_at) based on interval '3 hour'.
tsrange range function, third paramter, you can set the range bound be inclusive or not.
group by custom tsrange then get the max value of value if custome tsrange intersect with test6's tsrange.
Almost identical to your expected result.
WITH cte AS (
SELECT
tsrange(s, s + interval '3 hour', '[)') AS RANGE
FROM ((
SELECT
generate_series('2022-11-01 16:00:00'::timestamp, max(finish_at), interval '3 hour')
FROM
test6)
UNION (
SELECT
'2022-11-01 10:00:00'::timestamp)) s (s))
SELECT
RANGE,
max(value) FILTER (WHERE RANGE && tsrange IS TRUE)
FROM
cte
CROSS JOIN test6v
GROUP BY
RANGE
ORDER BY
RANGE;