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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 test(
id SERIAL PRIMARY KEY,
num int,
t text,
constraint u_constrainte unique (num, t)
)
CREATE TABLE
insert into test(num, t)
select i, 'test' from generate_series(1, 10) as t(i)
INSERT 0 10
select *
from test
| id | num | t |
|---|---|---|
| 1 | 1 | test |
| 2 | 2 | test |
| 3 | 3 | test |
| 4 | 4 | test |
| 5 | 5 | test |
| 6 | 6 | test |
| 7 | 7 | test |
| 8 | 8 | test |
| 9 | 9 | test |
| 10 | 10 | test |
SELECT 10
update test set num = num - 1
UPDATE 10
select *
from test
| id | num | t |
|---|---|---|
| 1 | 0 | test |
| 2 | 1 | test |
| 3 | 2 | test |
| 4 | 3 | test |
| 5 | 4 | test |
| 6 | 5 | test |
| 7 | 6 | test |
| 8 | 7 | test |
| 9 | 8 | test |
| 10 | 9 | test |
SELECT 10
update test set num = num + 1
ERROR: duplicate key value violates unique constraint "u_constrainte" DETAIL: Key (num, t)=(1, test) already exists.
select *
from test
| id | num | t |
|---|---|---|
| 1 | 0 | test |
| 2 | 1 | test |
| 3 | 2 | test |
| 4 | 3 | test |
| 5 | 4 | test |
| 6 | 5 | test |
| 7 | 6 | test |
| 8 | 7 | test |
| 9 | 8 | test |
| 10 | 9 | test |
SELECT 10