By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
Help with an interesting Postgres question: Why isn't an Index Only Scan used on a partition accessed via the parent table?.
CREATE TABLE
INSERT 0 5
| x | y | stone |
|---|---|---|
| 1 | 1 | W |
| 1 | 2 | W |
| 1 | 3 | W |
| 3 | 3 | B |
| 5 | 2 | B |
SELECT 5
| x | y | stone | group_number |
|---|---|---|---|
| 1 | 1 | W | 1 |
| 1 | 2 | W | 1 |
| 1 | 3 | W | 1 |
| 3 | 3 | B | 4 |
| 5 | 2 | B | 5 |
SELECT 5