Postgres 15

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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 t(t_id int);
insert into t values (1),(2),(3),(4);
create table u(u_id int);
insert into u values (5),(6),(7);
create table v(v_id int);

CREATE TABLE

INSERT 0 4

CREATE TABLE

INSERT 0 3

CREATE TABLE

select * from t,u

t_id
u_id

1
5

1
6

1
7

2
5

2
6

2
7

3
5

3
6

3
7

4
5

4
6

4
7

SELECT 12

select * from t FULL OUTER JOIN u ON FALSE

t_id
u_id

null
5

null
6

null
7

1
null

2
null

3
null

4
null

SELECT 7

select * from t,v

t_id
v_id

SELECT 0

select * from t FULL OUTER JOIN v ON FALSE

t_id
v_id

1
null

2
null

3
null

4
null

SELECT 4

t_id	u_id
null	5
null	6
null	7
1	null
2	null
3	null
4	null

t_id	v_id
1	null
2	null
3	null
4	null