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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 雞腿組 (
id int not null primary key
, val int
);
create table 排骨組 (
id int not null primary key
, val int
);
insert into 雞腿組
select n, 6 + 10 * n
from generate_series(1, 10) n;
insert into 排骨組
select n, 4 + 10 * n
from generate_series(1, 10) n;
select id, val
, rank() over(order by val desc)
from 雞腿組;
CREATE TABLE
CREATE TABLE
INSERT 0 10
INSERT 0 10
| id | val | rank |
|---|---|---|
| 10 | 106 | 1 |
| 9 | 96 | 2 |
| 8 | 86 | 3 |
| 7 | 76 | 4 |
| 6 | 66 | 5 |
| 5 | 56 | 6 |
| 4 | 46 | 7 |
| 3 | 36 | 8 |
| 2 | 26 | 9 |
| 1 | 16 | 10 |
SELECT 10
select 排骨組.val as 排骨組val
, rank(排骨組.val) WITHIN GROUP (order by 雞腿組.val desc) as 在雞腿組排名
from 雞腿組
, 排骨組
group by 排骨組.val
order by 排骨組.val desc;
| 排骨組val | 在雞腿組排名 |
|---|---|
| 104 | 2 |
| 94 | 3 |
| 84 | 4 |
| 74 | 5 |
| 64 | 6 |
| 54 | 7 |
| 44 | 8 |
| 34 | 9 |
| 24 | 10 |
| 14 | 11 |
SELECT 10