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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 mytable (
pub_date date
);
INSERT INTO mytable VALUES
('2023-01-02'),
('2023-01-10'),
('2023-01-31'),
('2023-02-01'),
('2023-02-02'),
('2023-02-03'),
('2023-02-04'),
('2023-02-10'),
('2023-03-02'),
('2023-03-02'),
('2023-03-02'),
('2023-03-02'),
('2023-03-02'),
('2023-03-02'),
('2023-04-10'),
('2023-04-15'),
('2023-04-20'),
('2023-04-21');
SELECT * FROM mytable;
CREATE TABLE
INSERT 0 18
| pub_date |
|---|
| 2023-01-02 |
| 2023-01-10 |
| 2023-01-31 |
| 2023-02-01 |
| 2023-02-02 |
| 2023-02-03 |
| 2023-02-04 |
| 2023-02-10 |
| 2023-03-02 |
| 2023-03-02 |
| 2023-03-02 |
| 2023-03-02 |
| 2023-03-02 |
| 2023-03-02 |
| 2023-04-10 |
| 2023-04-15 |
| 2023-04-20 |
| 2023-04-21 |
SELECT 18
SELECT
date_trunc('month', pub_date)::date as pub_month,
COUNT(*)
FROM mytable
GROUP BY 1
| pub_month | count |
|---|---|
| 2023-03-01 | 6 |
| 2023-01-01 | 3 |
| 2023-04-01 | 4 |
| 2023-02-01 | 5 |
SELECT 4
SELECT
*,
lag(count) OVER (ORDER BY pub_month) as prev_count
FROM (
SELECT
date_trunc('month', pub_date)::date as pub_month,
COUNT(*)
FROM mytable
GROUP BY 1
) s
| pub_month | count | prev_count |
|---|---|---|
| 2023-01-01 | 3 | null |
| 2023-02-01 | 5 | 3 |
| 2023-03-01 | 6 | 5 |
| 2023-04-01 | 4 | 6 |
SELECT 4
SELECT
*,
count * 100 / prev_count - 100
FROM (
SELECT
*,
lag(count) OVER (ORDER BY pub_month) as prev_count
FROM (
SELECT
date_trunc('month', pub_date)::date as pub_month,
COUNT(*)
FROM mytable
GROUP BY 1
) s
) s
| pub_month | count | prev_count | ?column? |
|---|---|---|---|
| 2023-01-01 | 3 | null | null |
| 2023-02-01 | 5 | 3 | 66 |
| 2023-03-01 | 6 | 5 | 20 |
| 2023-04-01 | 4 | 6 | -34 |
SELECT 4
SELECT
*,
(count * 100 / prev_count - 100)::text || '%'
FROM (
SELECT
*,
lag(count) OVER (ORDER BY pub_month) as prev_count
FROM (
SELECT
date_trunc('month', pub_date)::date as pub_month,
COUNT(*)
FROM mytable
GROUP BY 1
) s
) s
| pub_month | count | prev_count | ?column? |
|---|---|---|---|
| 2023-01-01 | 3 | null | null |
| 2023-02-01 | 5 | 3 | 66% |
| 2023-03-01 | 6 | 5 | 20% |
| 2023-04-01 | 4 | 6 | -34% |
SELECT 4