Substitute temporal gaps in result set with default value in Postgres - sql

Question

I'm using this query to average a value (performance) over 3-minute intervals of an hour:
SELECT
date_trunc('hour', created) AS created,
(extract(minute FROM created)::int / 3) minute_part,
worker,
AVG(performance)
FROM perf_stats
WHERE
group_id = 'foo' AND
worker = 'bar' AND
created > '1.1.2021 19:00:00' AND
created < '1.1.2021 20:00:00'
GROUP BY 1, 2, worker
ORDER BY 1, 2, worker;
This returns the following result set for the sample data set:
created
minute_part
worker
avg
2021-01-01 19:00:00
10
bar
3
Now I'd like to fill in zeros for the performance when there are no rows satisfying the query. Resulting in this result set:
created
minute_part
worker
avg
2021-01-01 19:00:00
0
bar
0
2021-01-01 19:00:00
1
bar
0
2021-01-01 19:00:00
2
bar
0
2021-01-01 19:00:00
3
bar
0
2021-01-01 19:00:00
4
bar
0
2021-01-01 19:00:00
5
bar
0
2021-01-01 19:00:00
6
bar
0
2021-01-01 19:00:00
7
bar
0
2021-01-01 19:00:00
8
bar
0
2021-01-01 19:00:00
9
bar
0
2021-01-01 19:00:00
10
bar
3
2021-01-01 19:00:00
11
bar
0
2021-01-01 19:00:00
12
bar
0
2021-01-01 19:00:00
13
bar
0
2021-01-01 19:00:00
14
bar
0
2021-01-01 19:00:00
15
bar
0
2021-01-01 19:00:00
16
bar
0
2021-01-01 19:00:00
17
bar
0
2021-01-01 19:00:00
18
bar
0
2021-01-01 19:00:00
19
bar
0
Table:
CREATE TABLE perf_stats
(
id BIGSERIAL NOT NULL PRIMARY KEY,
group_id TEXT NOT NULL,
worker TEXT NOT NULL,
performance DOUBLE PRECISION NOT NULL DEFAULT 0,
created TIMESTAMP NOT NULL
);
CREATE INDEX IDX_PERFSTATS_CREATED on perf_stats(group_id, created);
Sample Data:
INSERT INTO perf_stats (group_id, worker, performance, created)
VALUES('foo', 'bar', 2, '1.1.2021 19:30:00');
INSERT INTO perf_stats (group_id, worker, performance, created)
VALUES('foo', 'bar', 4, '1.1.2021 19:31:00');
I've experimented with generate_series but did not get it working so far.

Answer 1

You seem to want to generate rows for all the minutes. You can use generate_series() for this and then a LEFT JOIN:
SELECT date_trunc('hour', gs.ts) AS created,
(extract(minute FROM gs.ts)::int / 3) minute_part,
worker,
AVG(performance)
FROM generate_series('2021-01-01 19:00:00'::timestamp, '2021-01-01 20:00:00'::timestamp, interval '3 minute') gs(ts) LEFT JOIN
perf_stats ps
ON ps.group_id = 'foo' AND
ps.worker = 'bar' AND
ps.created >= gs.ts AND
ps.created < gs.ts + interval '3 minute'
GROUP BY 1, 2, worker
ORDER BY 1, 2, worker;