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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 level_one_table (
id int,
colmun1 varchar(10)
);
insert into level_one_table values
(1, 'va1');
create table level_two_table (
id int,
fk_level_one_id int,
colmun2 varchar(10)
);
insert into level_two_table values
(1, 1, 'va1'),
(2, 1, 'va2');
create table level_three_table (
id int,
fk_level_two_id int,
colmun3 varchar(10)
);
insert into level_three_table values
(1, 1, 'va1'),
(2, 2, 'va2');
CREATE TABLE
INSERT 0 1
CREATE TABLE
INSERT 0 2
CREATE TABLE
INSERT 0 2
SELECT jsonb_pretty(
json_build_object(
'level_one_table',
json_build_object(
'id', t0.id,
'level_two_table',
json_arrayagg(
json_build_object(
'id', t1.id,
'colmun2', t1.colmun2,
'level_three_table',
json_build_object(
'id', t2.id,
'colmun3', t2.colmun3
)
)
)
)
)::jsonb
) as json_obj
FROM level_one_table t0
LEFT JOIN level_two_table t1 ON t0.id = t1.fk_level_one_id
LEFT JOIN level_three_table t2 ON t1.id = t2.fk_level_two_id
GROUP BY t0.id
| json_obj |
|---|
| { "level_one_table": { "id": 1, "level_two_table": [ { "id": 1, "colmun2": "va1", "level_three_table": { "id": 1, "colmun3": "va1" } }, { "id": 2, "colmun2": "va2", "level_three_table": { "id": 2, "colmun3": "va2" } } ] } } |
SELECT 1