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Help with an interesting Postgres question: Why isn't an Index Only Scan used on a partition accessed via the parent table?.
create table pages (
date date,
pageviews int
);
insert into pages values
('2020-02-01'::date, 42),
('2020-02-02'::date, 3),
('2020-02-03'::date, 216),
('2020-02-04'::date, 186),
('2020-02-05'::date, 510),
('2020-02-06'::date, 419),
('2020-02-07'::date, 64),
('2020-02-09'::date, 230)
;
create table weights (
idx int,
weight float
);
insert into weights values
(0, 1/3.),
(1, 1/3.),
(2, 1/3.)
;
SELECT pages.date,
max(pages.pageviews) as pageviews,
CASE WHEN pages.date - (select min(date) from pages) >= 2 THEN sum(weight * ma_pages.pageviews) END as weighted_moving_average
FROM pages
JOIN pages AS ma_pages ON pages.date - ma_pages.date BETWEEN 0 AND 2
JOIN weights ON idx = pages.date - ma_pages.date
CREATE TABLE
INSERT 0 8
CREATE TABLE
INSERT 0 3
| date | pageviews | weighted_moving_average |
|---|---|---|
| 2020-02-01 | 42 | null |
| 2020-02-02 | 3 | null |
| 2020-02-03 | 216 | 87 |
| 2020-02-04 | 186 | 135 |
| 2020-02-05 | 510 | 304 |
| 2020-02-06 | 419 | 371.666666666667 |
| 2020-02-07 | 64 | 331 |
| 2020-02-09 | 230 | 98 |
SELECT 8